Search

I present an analysis of starspot modulation and flares in the TESS light curves of 112 M dwarfs with a TESS magnitude, {"references":["Stelzer, Beate et al. (2016). A path towards understanding the rotation-activity relation of M dwarfs with K2 mission, X-ray and UV data. MNRAS, 463, 1844","Raetz, Stefanie et al. (2020). Rotation-activity relations and flares of M dwarfs with K2 long- and short-cadence data. A&A, 637, A22","Hawley, Suzanne et al. (2014). Kepler Flares. I. Active and Inactive M Dwarfs. ApJ, 797, 121","Kaltenegger, L. et al. (2019). TESS Habitable Zone Star Catalog . ApJ, 874, L8"]}

A haiku about this work: K dwarfs are awesome HST has been staring Cool science in store! Efforts to discover and characterize habitable zone planets have primarily focused on Sun-like stars and M dwarfs. Yet the intermediate K stars provide an appealing compromise between these two extremes that has been relatively unexplored. Compared to solar-type stars, K stars are more abundant, maintain longer main-sequence lifetimes, and their planets are more suitable to observations based on the mass and radius ratios of the planet to star. While M stars also excel in these regards, they have been observed to have frequent flares with ultraviolet (UV) energies over 100 times greater than anything observed in the recent history of our Sun. Therefore, K stars may provide "super-habitable" environments for exoplanets that are more easily detectable and characterizable. Understanding the UV radiation incident on planets is pivotal in determining the habitability of any planets orbiting these stars, as well as our ability to observe any potential biosignatures in their atmospheres. With this aim, we observed a sample of K stars in the near-UV and far-UV at three representative ages using the Cosmic Origins Spectrograph on the Hubble Space Telescope (HST) to spectroscopically analyze the UV evolution of K stars. Here, we present the first results of this HST program. We will discuss the evolution of both the continuum and line emission from K stars from ages 40 Myr to ~Gyrs, representing key periods in planetary atmospheric formation., This work was funded by the NASA FINESST award, number 19-ASTRO20-0081.

M dwarfs are key targets for high-resolution spectroscopic analyses due to a high incidence of these stars in the solar neighbourhood and their importance as exoplanetary hosts. Several methodological challenges make such analyses difficult, leading to significant discrepancies in the published results. We compare M dwarf parameters derived by recent high-resolution near-infrared studies with each other and with fundamental stellar parameters. We also assess to what extent deviations from local thermodynamic equilibrium (LTE) for Fe and K influence the outcome of these studies. We carry out line formation calculations based on a modern model atmosphere grid along with a synthetic spectrum synthesis code that treats formation of atomic and molecular lines in cool-star atmospheres including departures from LTE. We use near-infrared spectra collected with the CRIRES instrument at the ESO VLT as reference observational data. We find that the effective temperatures obtained by the different studies mostly agree to better than 100 K. We see a much worse agreement in the surface gravities and metallicities. We demonstrate that non-LTE effects are negligible for Fe I in M-dwarf atmospheres but are important for K I. These effects, leading to K abundance and metallicity corrections on the order of 0.2 dex, may be responsible for some of the discrepancies in the published analyses. Differences in the temperature-pressure structures of the atmospheric models may be another factor contributing to the discrepancies, in particular at low metallicities and high effective temperatures. In high-resolution spectroscopic studies of M dwarfs attention should be given to details of the line formation physics as well as input atomic and molecular data. Collecting high-quality, wide wavelength coverage spectra of benchmark M dwarfs is an essential future step., Comment: 20 pages, 11 figures. Accepted in A&A

We present preliminary results of the study of three large long-duration flares detected on the active M-dwarf binary EQ~Peg using the Soft X-ray Telescope of the AstroSat observatory. The peak X-ray luminosities of the flares in the 0.3--7 keV band are found to be $\sim$4--10~$\times~10^{30}$ erg s$^{-1}$. Spectral analysis indicates that the corona of EQ~Peg has three dominant temperatures, with the first two plasma temperatures remaining constant during all the flares and the post-flare observation at $\sim$3 and $\sim$11~MK. The flare temperature peaked at 56, 40, and 31~MK, which are 2.5, 1.8, and 1.4 times the minimum value. The peak emission measures are found to be 1.16--5.64~$\times~10^{53}$~cm$^{-3}$, whereas the elemental abundances peaked at 0.7--1.2 times the solar abundances. Using quasi-static loop modeling, we estimated the loop lengths for all the flares to be on the order of $10^{11}$~cm. The estimated energies of all three flares are $>10^{33-35}$~erg, which put them in the category of superflare. Our study indicates that all three flares on EQ~Peg are associated with coronal mass ejections (CMEs). We estimated the CME mass and outward velocity of the CME mass are on the order of $10^{19}$~g and $\sim$5800--6500~km~s$^{-1}$, respectively. All three superflares are also found to be the longest duration flares ever observed on EQ~Peg., {"references":["Aarnio, A. N., Matt, S. P., & Stassun, K. G. 2012, ApJ, 760, 9.","Anders, E. & Grevesse, N. 1989, Geochimica Cosmochim- ica Acta, 53, 197.","Arnaud, K. A. 1996, In Astronomical Data Analysis Software and Systems V, edited by G. H. Jacoby & J. Barnes, Astro- nomical Society of the Pacific Conference Series, vol. 101, p. 17.","Bailer-Jones, C. A. L., Rybizki, J., Fouesneau, M., Mantelet, G., & Andrae, R. 2018, AJ, 156, 58.","Drake, J. J., Cohen, O., Yashiro, S., & Gopalswamy, N. 2013, ApJ, 764, 170.","Favata, F., Reale, F., Micela, G., Sciortino, S., Maggio, A., et al. 2000, A&A, 353, 987.","Fleming, T. A., Giampapa, M. S., Schmitt, J. H. M. M., & Book- binder, J. A. 1993, ApJ, 410, 387.","Haisch, B. M., Butler, C. J., Doyle, J. G., & Rodono, M. 1987, A&A, 181, 96.","Karmakar S. et al., 2016, MNRAS, 459, 3112","Karmakar, S., Pandey, J. C., Airapetian, V. S., & Misra, K. 2017, ApJ, 840, 102.","Karmakar, S., Rajpurohit, A. S., Allard, F., & Homeier, D. 2020, MNRAS, 498, 737.","Katsova, M. M., Livshits, M. A., & Schmitt, J. H. M. M. 2002, In Stellar Coronae in the Chandra and XMM-NEWTON Era, edited by F. Favata & J. J. Drake, Astronomical Society of the Pacific Conference Series, vol. 277, p. 515.","Lacy, C. H., Moffett, T. J., & Evans, D. S. 1976, ApJS, 30, 85.","Liefke, C., Ness, J.-U., Schmitt, J. H. M. M., & Maggio, A. 2008, A&A, 491, 859.","Morin, J., Donati, J.-F., Petit, P., Delfosse, X., Forveille, T., et al. 2008, MNRAS, 390, 567.","Morrison, R. & McCammon, D. 1983, ApJ, 270, 119.","Norton, A. J., Wheatley, P. J., West, R. G., Haswell, C. A., Street, R. A., et al. 2007, A&A, 467, 785","Pallavicini, R., Kundu, M. R., & Jackson, P. D. 1986, EXOSAT Detection of a Very Large Flare on EQ Peg, vol. 254, p. 225.","Pallavicini, R., Tagliaferri, G., & Stella, L. 1990, A&A, 228, 403.","Parsamyan, E. S. 1995, Astrophysics, 38, 206.","Pettersen, B. R. 1976, Institute of Theoretical Astrophysics Blindern Oslo Reports, 46, 1.","Pizzolato, N., Maggio, A., Micela, G., Sciortino, S., & Ventura, P. 2003, A&A, 397, 147.","Robrade, J., Ness, J. U., & Schmitt, J. H. M. M. 2004, A&A, 413, 317.","Robrade, J. & Schmitt, J. H. M. M. 2005, A&A, 435, 1073.","Schaefer, B. E., King, J. R., & Deliyannis, C. P. 2000, ApJ, 529, 1026.","Schmitt, J. H. M. M., Reale, F., Liefke, C., Wolter, U., Fuhrmeister, B., et al. 2008, A&A, 481, 799.","Shibayama, T., Maehara, H., Notsu, S., Notsu, Y., Nagao, T., et al. 2013, ApJS, 209, 5","Singh, K. P., Stewart, G. C., Westergaard, N. J., Bhat- tacharayya, S., Chandra, S., et al. 2017, Journal of Astro- physics and Astronomy, 38, 29.","Smith, R. K., Brickhouse, N. S., Liedahl, D. A., & Raymond, J. C. 2001, ApJL, 556, L91.","Tsuboi, Y., Imanishi, K., Koyama, K., Grosso, N., & Mont- merle, T. 2000, ApJ, 532, 1089.","Tu, Z.-L., Yang, M., Zhang, Z. J., & Wang, F. Y. 2020, ApJ, 890, 46.","van den Oord, G. H. J. & Mewe, R. 1989, A&A, 213, 245."]}

The dynamical origins of the intense magnetic activity exhibited by most M-dwarf stars must be tied to their internal convective dynamos, and yet there remain many unanswered questions concerning its details. Despite the central role magnetic flux ropes are thought to play in the formation of solar and stellar starspots, global MHD simulations of stellar interiors have historically struggled to self-consistently capture their dynamics. By their nature, these structures tend to be short-lived or wholly absent in all but the most turbulent high-resolution simulations -- environments which make their hand-identification and study prohibitively time-consuming. We present here a novel machine-learning pipeline for the autonomous identification and analysis of self-consistent, rising flux ropes found in our global 3D MHD simulations of M-dwarf convective interiors. We report on the details of the models developed, as well as early results from the project and its prospects moving forward., {"references":["Augustson, K.C. et al. (2015), ApJ 809 149","Bice, C.P. & Toomre, J. (2020), ApJ 893 107","Brown, B.P. et al. (2010), ApJ 711 424","Brown, B.P. et al. (2011), ApJ 731 69","Brown, B.P. et al. (2020), ApJL 902 L3","Browning, M.K. et al. (2008), ApJ 676 1262","Carlsson, M. et al. (2016), A&A 585 A4","Davenport, J.R.A. (2016), ApJ 829 23","Fan, Y. & Fang, F. (2014), ApJ 789 13","Featherstone, N.A. & Hindman, B.W. (2016), ApJ 818 32","Guerrero, G. et al (2016), ApJL 828 L3","Kowalski, A.F. et al. (2009), ApJ 138 633","Kowalski, A.F. et al. (2010), ApJL 714 L98","Krizhevsky, A. et al. (2017), Commun. ACM 60 84","Martinez-Sykora, J. et al. (2012), ApJ 753 161","Matilsky, L.I. & Toomre, J. (2020), ApJ 892 106","Nelson, N.J. et al. (2011), ApJL 739 L38","Nelson, N.J. et al. (2013), ApJ 762 73","Nelson, N.J. et al. (2014), SoPh 289 441","Rempel, M. (2012), ApJ 750 62","Silverberg, S.M. et al. (2016), ApJ 829 129","Strugarek, A. et al. (2018), ApJ 863 35","Weber, M.A. & Browning, M.K. (2016), ApJ 827 95","West, A.A. et al. (2008), ApJ 135 785","West, A.A. et al. (2015), ApJ 812 3","Xia, X. & Kulis, B. (2017), arxiv:1711.08506","Yadav, R.K. et al. (2015), ApJL 813 L31","Zinkevich, M. et al. (2010), NIPS 4 4"]}

Kepler's extended mission (K2) Earth-sized planetary legacy is a niche that still remains to be fully exploited. We reanalyzed all light curves in K2 C1-C8, C12-C18 campaigns with a wavelet-based detrending method TFAW developed by our team, and the period search algorithm TLS. The combination of these two methods allows to detect and characterize planetary transit candidates around fainter targets ($12.5 < K_{p} < 18.5$) than any previous study. We present 220 new planetary candidates as a result of a preliminary survey. All of them have passed a vetting procedure including: candidate periods with SDE$_{TLS}>$9.0, visual inspection of the candidate light curve, inspection of archival Pan-STARRS1 images and Gaia DR2 to discard close stellar companions and statistical FPP We assigned our candidates sample three levels of priority: six top-priority detected in two or more separate but overlapping K2 campaigns, 110 high-priority meeting the above requirements, and 104 low-priority still meeting the same requirements, but having either FPP close to 2% or pending further reanalysis. The bulk of our TFAW K2 survey are small planet candidates with $R_{p}, {"references":["Armstrong, D. J., Kirk, J., Lam, K. W. F., McCormac, J., Osborn, H. P.,et al.2016, MNRAS, 456, 2260","Armstrong, D. J., Kirk, J., Lam, K. W. F., McCormac, J., Walker,S. R.,et al.2015, A&A, 579, A19","Claret, A. 2018, A&A, 618, A20","Crosseld, I. J. M., Ciardi, D. R., Petigura, E. A., Sinuko, E.,Schlieder, J. E.,et al.2016, ApJS, 226, 7","del Ser, D. & Fors, O. 2020, MNRAS, 498, 2778","del Ser, D., Fors, O., & Núñez, J. 2018, A&A, 619, A86","Gaia Collaboration, Brown, A. G. A., Vallenari, A., Prusti, T.,de Bruijne, J. H. J.,et al.2018, A&A, 616, A1","Hardegree-Ullman, K. K., Zink, J. K., Christiansen, J. L.,Dressing, C. D., Ciardi, D. R.,et al.2020, ApJS, 247, 28","Heller, R., Hippke, M., & Rodenbeck, K. 2019, A&A, 627, A66","Hippke, M. & Heller, R. 2019, A&A, 623, A39","Huang, C. X., Vanderburg, A., Pál, A., Sha, L., Yu, L.,et al.2020, Research Notes of the American Astronomical Soci-ety, 4, 206","Kruse, E., Agol, E., Luger, R., & Foreman-Mackey, D. 2019,ApJS, 244, 11","Luger, R., Kruse, E., Foreman-Mackey, D., Agol, E., & Saun-ders, N. 2018, AJ, 156, 99","Mayo, A. W., Vanderburg, A., Latham, D. W., Bieryla, A.,Morton, T. D.,et al.2018, AJ, 155, 136","Morton, T. D. 2012, ApJ, 761, 6","Vanderburg, A., Latham, D. W., Buchhave, L. A., Bieryla, A.,Berlind, P.,et al.2016, ApJS, 222, 14"]}

In the light of more and more new instrumentation to get a deeper insight into the universe, tons of data are collected. While traditional machine-learning methods have been used in processing stellar spectral data, such large new datasets are better handled with Deep Learning (DL) techniques. In this work, we present a Deep Convolutional Neural Network (CNN) approach to derive fundamental stellar parameters (effective temperature, surface gravity, metallicity and rotational velocity) from high-resolution high signal-to-noise ratio spectra. We construct an individual CNN architecture for each of the four parameters and train them on synthetic PHOENIX-ACES spectra. After that, we apply the trained networks to the observed spectra of 50 M dwarfs observed with CARMENES. The CARMENES spectrograph, installed on the 3.5 m telescope at the Calar Alto Observatory (Spain) has two channels, covering the visible (0.52 to 0.96 µm, R = 96,400) and near-infrared (0.96 to 1.71 µm, R = 80,600) spectral ranges. We compare our results to literature values, and demonstrate that our method can be used for stellar parameter determination without the need of having a huge sample of stellar spectra with known parameters, because our networks can be trained on synthetic spectra. Introducing Deep Transfer Learning (DTL) in our approach allows us to transfer external knowledge about the stellar parameters (e.g., from interferometry) to our training set and therefore improve our results compared to literature.&nbsp

In the light of more and more new instrumentation to get a deeper insight into the universe, tons of data are collected. While traditional machine-learning methods have been used in processing stellar spectral data, such large new datasets are better handled with Deep Learning (DL) techniques. In this work, we present a Deep Convolutional Neural Network (CNN) approach to derive fundamental stellar parameters (effective temperature, surface gravity, metallicity and rotational velocity) from high-resolution high signal-to-noise ratio spectra. We construct an individual CNN architecture for each of the four parameters and train them on synthetic PHOENIX-ACES spectra. After that, we apply the trained networks to the observed spectra of 50 M dwarfs observed with CARMENES. The CARMENES spectrograph, installed on the 3.5 m telescope at the Calar Alto Observatory (Spain) has two channels, covering the visible (0.52 to 0.96 µm, R = 96,400) and near-infrared (0.96 to 1.71 µm, R = 80,600) spectral ranges. We compare our results to literature values, and demonstrate that our method can be used for stellar parameter determination without the need of having a huge sample of stellar spectra with known parameters, because our networks can be trained on synthetic spectra. Introducing Deep Transfer Learning (DTL) in our approach allows us to transfer external knowledge about the stellar parameters (e.g., from interferometry) to our training set and therefore improve our results compared to literature., {"references":["Abadi et al. (2015), https://github.com/tensorflow/tensorflow","Abraham et al. (2018), 10.1093/mnras/sty627","Anthony and Bartlett (2009), ISBN9780521118620","Antoniadis-Karnavas et al. (2020), 10.1051/0004-6361/201937194","Birky et al. (2020), 10.3847/1538-4357/ab7004","Boyajian et al. (2008), 10.1086/589554","Boyajian et al. (2012), 10.1088/0004-637x/757/2/112","Bressan et al. (2012), 10.1111/j.1365-2966.2012.21948.x","Chen et al. (2014), 10.1093/mnras/stu1605","Chen et al. (2015), 10.1093/mnras/stv1281","Chollet (2015), \\url{https://github.com/keras-team/keras}","Czesla et al. (2019), ascl:1906.010","Dieleman et al. (2015), 10.1093/mnras/stv632","Dittmann et al. (2016), 10.3847/0004-637x/818/2/153","Fabbro et al. (2018), 10.1093/mnras/stx3298","Figueira et al. (2016), 10.1051/0004-6361/201526900","Freedman and Diaconis (1981), 10.1007/BF01025868","Gaidos and Mann (2014), 10.1088/0004-637X/791/1/54","Gong and Ordieres-Meré (2016), 10.1016/j.envsoft.2016.06.020","Hauschildt (1992), 10.1016/0022-4073(92)90105-D","Hauschildt (1993), 10.1016/0022-4073(93)90080-2","Hauschildt and Baron (1999), arXiv:astro-ph/9808182","Hon et al. (2017), 10.1093/mnras/stx1174","Houdebine et al. (2019), 10.3847/1538-3881/ab23fe","Husser et al. (2013), 10.1051/0004-6361/201219058","LeCun et al. (2015), 10.1038/nature14539","Mahabal et al. (2017), arXiv:1709.06257","Maldonado et al. (2015), 10.1051/0004-6361/201525797","Mann et al. (2015), 10.1088/0004-637X/804/1/64","McInnes et al. (2018), 10.21105/joss.00861","Montes et al. (2018), 10.1093/mnras/sty1295","Nagel et al. (2021), submitted to A&A","Ness et al. (2015), 10.1088/0004-637X/808/1/16","Parzen (1962), 10.1214/aoms/1177704472","Passegger et al. (2018), 10.1051/0004-6361/201732312","Passegger et al. (2019), 10.1051/0004-6361/201935679","Passegger et al. (2020), 10.1051/0004-6361/202038787","Quirrenbach et al. (2018), 10.1117/12.2313689","Reiners et al. (2018), 10.1051/0004-6361/201732054","Rojas-Ayala et al. (2012), 10.1088/0004-637X/748/2/93","Rosenblatt (1956), 10.1214/aoms/1177728190","Sarro et al. (2018), 10.1093/mnras/sty165","Schmidhuber (2015), 10.1016/j.neunet.2014.09.003","Scott (1979), 10.1093/biomet/66.3.605","Tang et al. (2014), 10.1093/mnras/stu2029","Terrien et al. (2015), 10.1088/2041-8205/802/1/l10","Vilalta (2018), 10.1088/1742-6596/1085/5/052014","vonBraun et al. (2014), 10.1093/mnras/stt2360","Whitten et al. (2019), 10.1051/0004-6361/201833368","Wu et al. (2018), 10.1093/mnras/sty2646","Zechmeister et al. (2018), 10.1051/0004-6361/201731483","Zhang et al. (1998), 10.1016/S0169-2070(97)00044-7","Zheng et al. (2018), 10.3390/s18072146"]}

Over 4000 exoplanets have been discovered in the past 25 years or so, most of which orbit cool stars. Star-planet tidal interactions are known to drive the late evolution of the shortest-period planetary systems via tidal dissipation. Such dissipation is known to vary considerably with the mass, age, rotation, and metallicity of the star. To quantify tidal dissipation as accurately as possible, two key physical mechanisms need to be further explored : stellar differential rotation and magnetism in convective regions, which have been constrained in cool stars by ground-based spectropolarimetric observations as well as space-based asteroseismic observations. In this contribution, we report our recent progress on the investigation of the impact of stellar differential rotation and magnetism on the dynamics and dissipation of tidal inertial waves, along the evolution of low-mass stars. First, we show that a large-scale magnetic field has a negligible effect on the excitation of tidal waves whereas it deeply impacts the dissipation mechanism of tidal waves in the convective envelope of all cool stars all along their evolution. Then, by developing a local shearing box model of a small patch of the convective shell, we demonstrate how tidal waves can be either fully transmitted, damped, or even amplified at the so-called critical layers (when the phase speed of the wave is equal to the local velocity of the fluid), that has potentially strong implications for angular momentum exchanges between tidal waves and zonal flows, and ultimately for the evolution of planetary systems., {"references":["Lin & Ogilvie (2019). DOI:10.1093/mnras/stx2764","Amard et al. (2019). DOI: 10.1051/0004-6361/201935160","See et al. (2019). DOI: 10.3847/1538-4357/ab46b2","Astoul et al. (2019). DOI: 10.1051/0004-6361/201936477","Brun et al. (2017). DOI: 10.3847/1538-4357/aa5c40","Astoul et al. (2021). DOI: 10.1051/0004-6361/202039148"]}

For more than thirty years, radio astronomers have searched for auroral emission from exoplanets. With the Dutch radio telescope LOFAR we have recently detected strong, highly circularly polarised low-frequency (144 MHz) radio emission associated with a M-dwarf - the expected signpost of such radiation. The star itself is quiescent, with a 130-day rotation period and low X-ray luminosity. In this talk, I will detail how the radio properties of the detection imply that such emission is generated by the presence of an exoplanet in a short period orbit around the star. I will also discuss how our LOFAR observations represents the most comprehensive survey of stellar systems at low frequencies, and the implications of this new population we have detected in understanding the magnetosphere of M dwarfs and exoplanetary magnetic fields.

For more than thirty years, radio astronomers have searched for auroral emission from exoplanets. With the Dutch radio telescope LOFAR we have recently detected strong, highly circularly polarised low-frequency (144 MHz) radio emission associated with a M-dwarf - the expected signpost of such radiation. The star itself is quiescent, with a 130-day rotation period and low X-ray luminosity. In this talk, I will detail how the radio properties of the detection imply that such emission is generated by the presence of an exoplanet in a short period orbit around the star. I will also discuss how our LOFAR observations represents the most comprehensive survey of stellar systems at low frequencies, and the implications of this new population we have detected in understanding the magnetosphere of M dwarfs and exoplanetary magnetic fields.

For more than thirty years, radio astronomers have searched for auroral emission from exoplanets. With the Dutch radio telescope LOFAR we have recently detected strong, highly circularly polarised low-frequency (144 MHz) radio emission associated with a M-dwarf - the expected signpost of such radiation. The star itself is quiescent, with a 130-day rotation period and low X-ray luminosity. In this talk, I will detail how the radio properties of the detection imply that such emission is generated by the presence of an exoplanet in a short period orbit around the star. I will also discuss how our LOFAR observations represents the most comprehensive survey of stellar systems at low frequencies, and the implications of this new population we have detected in understanding the magnetosphere of M dwarfs and exoplanetary magnetic fields.

In Rains et al. 2021 (arXiv:2102.08133) we conducted a medium resolution optical (3,500 < λ < 7,000 Å) spectroscopic survey of 92 cool (3,000 ≲ Teff ≲ 4,500 K) southern TESS candidate planet hosts and 136 cool dwarf standards using WiFeS on the ANU 2.3 m Telescope. As part of our model-based fitting methodology, we conducted an investigation into MARCS model atmospheres and found they systematically overestimate flux the cooler the star and bluer the wavelength. In addition, we developed an updated photometric [Fe/H] calibration with Gaia+2MASS photometry for isolated main sequence stars precise to ±0.19 dex. This was built upon a calibration sample of 69 cool dwarfs in binary systems with a hotter FGK companion, valid from super-solar to metal poor, and over 1.51 < Gaia BP‒RP < 3.3.

Stellar age is a key fundamental property for understanding the history, evolution, and future of stellar populations, the Milky Way, and exoplanets. However, age is extremely difficult to measure for individual stars. Low-mass stars, or M dwarfs, are the most numerous stars in the Galaxy, they have lifetimes longer than the current age of the Universe, and are likely to host the majority of Earth-like exoplanets. For this reason, these main sequence stars are ideal for studying the Milky Way and exoplanets properties in a wide range of ages. Ages of M dwarfs are especially difficult to estimate because methods used for solar-type stars break down as lower mass objects become fully convective. Empirical and statistical methods are required to constrain the ages of M dwarfs. I want to build a robust Bayesian algorithm to infer ages of M dwarfs from three age indicators: 1) Position in the color–magnitude diagram; 2) Magnetic activity, as indicated by H𝛼 emission line strength; 3) Full kinematics, taking advantage of Gaia DR2. I will present the age-calibrations I did of these age indicators, including the age-activity relation for H𝛼. I will show the results we obtained from our calibration of the age-activity relation, which indicates that H𝛼 strength decrease with age. I will also explain how we are going to use this relation to obtain precise estimation of M dwarf ages., {"references":["Bochanski et al. 2010, AJ, 139, 2679","Dressing & Charbonneau 2015, ApJ, 807","Gagné et al. 2018, ApJ, 856, 23"]}

The coeval and co-evolving members of globular clusters serve as stellar astrophysics laboratories, as otherwise inaccessible parameters such as age and composition are often restricted within the cluster and may be inferred from its colour-magnitude diagrams. Until recently, the typically large distances of globular clusters confined such studies to their most massive members. Now, the promise of highly sensitive ground- and space-based facilities will extend the reach of these studies into the substellar regime. We are investigating the elemental abundances of stars in one of the closest and most well-studied globular clusters, ω Centauri, using a new grid of synthetic spectra and colour-magnitude diagrams produced with a custom combination of ATLAS and PHOENIX 15 model atmospheres and the MESA evolutionary code (within the MIST framework). To our knowledge, these new models yield the best agreement with HST photometry, and emphasize the importance of atmosphere-interior coupling at low effective temperatures. We find that α-elements enhancement in the abundances of ultracool dwarfs plays a key role in determining their observable characteristics. Our models provide greater consistency in the colour-magnitude diagram between the most massive and least massive stars on the main sequence, although we find that the best-fit metallicity for the ultracool dwarfs is somewhat higher. Comprehensive treatment of molecules and clouds by the Settling formalism of the PHOENIX code enables us to assess the effects of gravity and composition on the formation of cloud layers. This allows us to extend model isochrones beyond the limit of existing photometric data. We make quantitative predictions for the colours and magnitudes of ω Centauri substellar population, which will inform observing strategies for future studies with JWST, TMT, GMT and ELT., {"references":["F. Allard, D. Homeier, and B. Freytag. In: Philosophical Transactions of the Royal Society of London Series A 370.1968 (June 2012)","F. Allard, P. H. Hauschildt, and A. Schweitzer. In: The Astrophysical Journal 539.1 (Aug. 2000).","J. Choi et al. In: The Astrophysical Journal 823.2, 102 (2016).","A. Dotter et al. In: The Astrophysical Journals 178.1 (Sept. 2008).","R. Gerasimov et al. In: Research Notes of the American Astronomical Society 4.12, 214 (Dec. 2020).","P. H. Hauschildt et al. In: 525.2 (Nov. 1999).","C. Helling et al. In: MNRAS 391.4 (Dec. 2008).","T. O. Husser et al. In: Astronomy & Astrophysics 553, A6 (2013).","R. L. Kurucz. In: SAO Special Report 309 (1970).","R. L. Kurucz. In: Determination of Atmospheric Parameters of B-, A-, F- and G-Type Stars GeoPlanet: Earth and Planetary Sciences (2014).","A. F. Marino et al. In: The Astrophysical Journal 746.1, 14 (2012).","A. P. Milone et al. In: MNRAS 469.1 (July 2017).","B. Paxton et al. In: The Astrophysical Journal Supplement Series 192.1 (2010).","A. Sollima, F. R. Ferraro, and M. Bellazzini. In: MNRAS 381.4 (Nov. 2007).","J. Soltis, S. Casertano, and A. G. Riess. In: The Astrophysical Journal 908.1, L5 (Feb. 2021)."]}

The propagation of Galactic cosmic rays is well studied in the context of the Sun but it is poorly known in the context of M dwarfs. Quantifying the flux of cosmic rays reaching exoplanets is essential since they are important in the context of life. Here, we investigate the modulation of Galactic cosmic rays as they travel through the astrosphere of six M dwarfs. We perform simulations using a combined 1D cosmic ray transport model and 1D MHD stellar wind model. We found that, three M dwarfs in our sample have Galactic cosmic rays fluxes comparable with Earth’s around their much closer-in habitable zones. Most of theknownexoplanetsin our samplehave a significantly lower flux of Galactic cosmic rays than values observed at the Earth. This includesGJ 273b which is the only known planet orbiting the habitable zone of its host star.

In this contribution we summarize our project devoted to identify activity-sensitive spectral lines in the CARMENES visible and near-infrared spectral range of M dwarfs. The aim is to contribute to solve the problem of stellar activity in RV measurements to search for exoplanets around these stars and in the determination of precise stellar parameters. To identify lines with a significant chromospheric contribution, apart from well known activity indicators (Na I D 1 D 2 He I D 3 Hα, and Ca II IRT lines, He I 10830 Å, Paγ and Paβ lines), we have used the spectral subtraction technique using our Python code iSTARMOD Labarga Montes 2020 choosing as reference the spectrum of the star with lower activity. We confirm the new activity sensitive lines by analysing the correlation with the other well known activity indicators in the same spectra and their temporal evolution in two particular active stars EV Lac (EV Lacertae, M 3.5) and YZ CMi (YZ Canis Minoris, M 4.5). They are specially active stars with strong flares and strong magnetic fields. In addition, we analyse line by line the template spectrum (co added of all the individual spectra available) of these two stars applying also the spectral subtraction using in this case as reference star an inactive M dwarf star of similar spectral type to search for magnetically sensitive lines, that is lines with detectable Zeeman broadening. After this analysis on YZ CMi and EV Lac, we have found 84 and 97 chromospheric activity-sensitive lines and 160 and 170 magnetically-sensitive spectral lines respectively. We are now studying the impact of the elimination of the activity sensitive spectral lines identified in this way on the RV determination using cross correlation functions with weighted binary masks as in Lafarga et al. (2020) and on the stellar parameters determination by spectral synthesis as in Marfil et al. (2021)., {"references":["Labarga , F. & Montes, D. 2020, in Contributions to the XIV.0 Scientific Meeting(virtual) of the Spanish Astronomical Society, 153","Lafarga, M. et al. 2020, A&A, 636, A36","Marfil et al. (2021) in prep."]}

The magnetic phenomena on the solar surface have been the subject of several investigations over the last 400 years. The early indicator of the solar magnetic activity was the sunspot counting. The main indicators now are the International Sunspot Number, the Group Number, the Total Sunspot Area, and Photometric Sunspot Index. Several improvements in observational techniques have allowed measuring the magnetic activity using the solar/stellar spectra. The standard spectroscopic activity indicator is the S-index, based on the Ca II H&K emission lines, jointly the chromospheric component R'HK. Observations to stellar spots in other stars remain unclear, it is worth proposing a theoretical estimate to spot amount on other solar-type stars using the Sun as a star. We report a calibration between the spectroscopic chromospheric activity proxies (S-index and R'HK) and the sunspot indicators over the last decades. Our results indicate a quadratic power-law relationship.

Stellar ultraviolet (UV) radiation has significant implications on habitability of their exoplanets, yet this radiation is partly unobservable due to interstellar medium absorption. We used the radiative transfer code SSRPM to build stellar models of two M dwarfs and synthesize their UV spectra, particularly focusing on the far-UV and extreme-UV spectra. Our most important findings are that 1) the coronae of two M dwarfs are responsible for more than half of their respective EUV fluxes, and 2) the continuum in the FUV band between 145 and 170 nm is responsible for about half of total emission in this band. Here, we discuss the significance of these results and outline future projects aimed to improve our understanding of solar and stellar UV emission.

Solar and stellar flares are caused by the sudden release of magnetic energy on the surfaces. In the case of the Sun, mass ejections often accompany solar flares and affect the Earth’s environment. Active solar-type stars (G-type main-sequence stars) sometimes show larger `superflares' (Maehara et al. 2012) that may cause more huge mass ejections than those of solar flares. The stellar mass ejections can greatly affect the exoplanet habitability and the stellar mass evolution (e.g. Airapetian et al. 2020). However, no observational indication of mass ejection has been reported especially for solar-type stars. We conducted spectroscopic monitoring observations of the active young solar analog EK Dra (a famous zero-age main-sequence G-dwarf) by our new 3.8-m Seimei telescope, simultaneously with TESS photometry. Our time-resolved optical spectroscopic observation shows clear evidence for a stellar mass ejection associated with a superflare on the solar-type star (Namekata et al. submitted). After the superflare brightening with the radiated energy of 2.0×1033erg observed by TESS, a blue-shifted H-alphaabsorption component with a velocity of -510km s-1appeared. The velocity gradually decayed in 2 hours and the deceleration 0.34 km s-2was consistent with the surface gravity on EK Dra (0.30 ±0.05 km s-2). The temporal changes in the spectra greatly resemble that of a solar mass ejection observed by the SMART telescope at Hida observatory. Moreover, the ejected mass of 1.1×1018g roughly corresponds to those predicted from solar flare-energy/ejected-mass relation. These discoveries imply that a huge stellar mass ejection occurs possibly in the same way as solar ones. Our high-quality dataset can be helpful for future studies to estimate its impacts on the young-planet atmosphere around young solar-type stars as well as stellar mass/angular momentum evolution.

In the canonical formulation of stellar magnetic dynamo theory, the tachocline in partially convective stars serves to arrange small scale randomly oriented fields, which are generated by stochastic movement of plasma, into a large scale coherent field. Mid-to-late M-dwarfs show more magnetic activity than classical magnetic dymano theory predicts. This leads to the open question: what mechanism generates and maintains these fields in fully convective stars? Mid-to-late M-dwarfs show tight correlations between rotation rates and magnetic activity, consistent with elements of classical dynamo theory. We use data from Magellan Inamori Kyocera Echelle (MIKE) Spectrograph to measure R'HK values for 50 spectroscopically identified M-dwarfs selected from the MEarth survey. These stars span spectral classes from M5.0 to M3.5 and have rotation periods ranging from hours to months. Here, we present the rotation–activity relationship as traced through these data. We find power law and saturated regimes consistent to within one sigma of previously published results, and find the saturated value to be mass-dependent., {"references":["Chabrier, G., & Baraffe, I. 1997, A&A, 327, 1039, Astudillo-Defru, N., Delfosse, X., Bonfils, X., et al. 2017, A&A, 600, A13, Wright, N. J., Newton, E. R., Williams, P. K. G., Drake, J. J., & Yadav, R. K. 2018, MNRAS, 479, 2351, Salvatier, J., Wiecki, T. V., & Fonnesbeck, C. 2016, PeerJComputer Science, 2, e55"]}

M dwarfs are considered one of the most likely places to find extraterrestrial life in part due to their large numbers in the nearby solar neighborhood. However, they have much more intense flaring events than stars like our Sun, which could negatively impact the habitability of close-in exoplanets. Our current understanding of the multi-wavelength connections of M dwarf flaring events is surprisingly far from complete, both in wavelength coverage and temporal resolution. To rectify this, our team collected multi-wavelength data of the dM1e flare star AU Mic over 7-days using a variety of telescopes. Here, we focus on data from XMM-Newton and the Las Cumbres Observatory Global Telescope (LCOGT) network. We discuss the Neupert effect among the X-ray, UV, and optical response in a sample of high-energy flares and present cumulative flare frequency distribution (CFFD) statistics. We find that AU Mic’s U-band CFFD is consistent with other M dwarfs in the literature and that the Neupert effect (i.e. the X-ray derivative peak and NUV peak timings overlap) is not present in all characterized flares. We propose a new Neupert classification system that includes Quasi-Neupert (response in X-ray and NUV, but the timings do not match) and Non-Neupert (missing a response from either X-ray or NUV). Future work on this project includes adding existing AU Mic radio and H-alpha observations to our analysis and using our RADYN flare modeling program to determine the electron beam heating, proton beam heating, and magnetic mirroring needed to reproduce the full range of multi-wavelength responses we see in observations., {"references":["Veronig, Astrid M. et al. (2005). Physics of the Neupert Effect: Estimates of the Effects of Source Energy, Mass Transport, and Geometry Using RHESSI and GOES Data.","Smith, David S. et al. (2004). Importance of Biologically Active Aurora-like Ultraviolet Emission: Stochastic Irradiation of Earth and Mars by Flares and Explosions.","Walker, A. R. (1981). Flare activity of proxima Cen.","Lacy, C. H. (1976). UV Ceti stars: statistical analysis of observational data.","McTiernan, James M. et al. (1999). The Solar Flare Soft X-Ray Differential Emission Measure and the Neupert Effect at Different Temperatures.","Veronig, Astrid M. et al. (2002). Investigation of the Neupert effect in solar flares. I. Statistical properties and the evaporation model.","Carlsson & Stein, (1997). Formation of Solar Calcium H and K Bright Grains.","Allred, Joel C. et al. (2015). A Unified Computational Model for Solar and Stellar Flares.","Gershberg, R. E. (1972). Some results of the cooperative photometric observations of the UV Cet-type flare stars in the years 1967 71.","Mitra-Kraev, U. et al. (2005). Relationship between X-ray and ultraviolet emission of flares from dMe stars observed by XMM-Newton","Kowalski, Adam F. et al (2013). Time-resolved Properties and Global Trends in dMe Flares from Simultaneous Photometry and Spectra."]}

The period versus mass diagrams (i.e., rotational sequences) of open clusters provide crucial constraints for angular momentum evolution studies. However, their memberships are often heavily contaminated by field stars, which could potentially bias the interpretations. In this paper, we use data from Gaia DR2 to re-assess the memberships of seven open clusters with ground- and space-based rotational data, and present an updated view of stellar rotation as a function of mass and age. We use the Gaia astrometry to identify the cluster members in phase-space, and the photometry to derive revised ages and place the stars on a consistent mass scale. Applying our membership analysis to the rotational sequences reveals that: 1) the contamination in clusters observed from the ground can reach up to $\sim 35\%$; 2) the overall fraction of rotational outliers decreases substantially when the field contaminants are removed, but some outliers persist; 3) there is a sharp upper edge in the rotation periods at young ages; 4) at young ages, stars in the 1.0-0.6 Msun range inhabit a global maximum of rotation periods, potentially providing an optimal window for habitable planets. Additionally, we see clear evidence for a strongly mass-dependent spin-down process. In the regime where rapid rotators are leaving the saturated domain, the rotational distributions broaden (in contradiction with popular models), which we interpret as evidence that the torque must be lower for rapid rotators than for intermediate ones. The cleaned rotational sequences from ground-based observations can be as constraining as those obtained from space., Comment: Accepted for publication in ApJS. 26 pages of main text, 14 figures, and 9 pages of appendices. Appendix machine-readable tables are available as ancillary files (they are displaced by one letter with respect to the previous version but are otherwise identical)

The validation and recovery of periodic signals in radial velocity data, especially low amplitude signals, is being complicated by the inherent stellar variations due to stellar activity. Using the time-series of high-resolution HARPS-N spectra of stars as well as the Sun, we are developing a new least-squares deconvolution method to determine at the same time a precise radial velocity and an independent measurement of the instantaneous line-of-sight magnetic flux on the visible stellar hemisphere. We present the new method as well as some first results.

Exoplanet detection with precise radial velocity (RV) observations is currently limited by spurious RV signals introduced by the host star in the form of stellar activity (i.e. faculae, starspots). Here we show that a cross-disciplinary approach blending solar physics, exoplanet astronomy, and computer science can help us further our understanding of stellar activity signals. Using machine learning techniques such as linear regression and neural networks, we demonstrate that we can significantly reduce the activity signals (primarily starspots/faculae) from real center-of-mass RV shifts. Previous efforts have focused on carefully filtering out activity signals in time using Gaussian process regression (e.g. Haywood et al. 2014). Instead, we separate activity signals from true center-of-mass RV shifts using only changes to the average shape of spectral lines, and no information about when the observations were collected. We have trained our machine learning models on both simulated data (generated with the SOAP 2.0 software; Dumusque et al. 2014) and observations of the Sun from the HARPS-N Solar Telescope (Dumusque et al. 2015; Phillips et al 2016; Collier Cameron et al. 2019). We find that these techniques can successfully predict and remove stellar activity from approximately 700 observations taken nearly daily over three years with the HARPS-N Solar Telescope, reducing the RV scatter from 1.47 m s-1 to 0.78 m s-1 (a 47% or factor of ~ 1.9 improvement). For the simulated data, these techniques can predict the stellar activity signal nearly exactly, reducing the RV scatter from 82.0 cm s-1 to 3.1 cm s-1 which suggests that we may be able to achieve more precise velocities when applied to data from newer stabilized spectrographs like ESPRESSO. In the future, these or similar techniques could remove activity signals from observations of stars outside our solar system and eventually help detect habitable-zone Earth-mass exoplanets around Sun-like stars., {"references":["Dumusque et al (2014). ApJ 796, 132.","Haywood PhD Thesis (2015), Univ. St Andrews, 172.","Mayor & Queloz (1995), Nature 378, 355, 1995.","Shallue & Vanderburg (2018), AJ 155, 94.","Cosentino et al (2012)."]}

In the canonical formulation of stellar magnetic dynamo theory, the tachocline in partially convective stars serves to arrange small scale randomly oriented fields, which are generated by stochastic movement of plasma, into a large scale coherent field. Mid-to-late M-dwarfs show more magnetic activity than classical magnetic dymano theory predicts. This leads to the open question: what mechanism generates and maintains these fields in fully convective stars? Mid-to-late M-dwarfs show tight correlations between rotation rates and magnetic activity, consistent with elements of classical dynamo theory. We use data from Magellan Inamori Kyocera Echelle (MIKE) Spectrograph to measureR'HKvalues for 50 spectroscopically identified M-dwarfs selected from the MEarth survey. These stars span spectral classes from M5.0 to M3.5 and have rotation periods ranging from hours to months. Here, we present the rotation–activity relationship as traced through these data. We find power law and saturated regimes consistent to within one sigma of previously published results, and find the saturated value to be mass-dependent.

We present current results from a project aiming to clarify how stellar winds evolve during the first billion years of the main sequence evolution of solar-type stars, and the implications for early solar evolution. This project is based on the extensive TOUPIES survey of stellar magnetic fields, with surface radial field maps used to model stellar winds via Space Weather Modelling Framework codes. We also explore numerical methods for producing wind models verifiable through direct comparisons with observations of the modern-day Sun. We find that a modelling approach used with solar magnetograms can be efficiently extended to survey a range of young solar-type stars with magnetic field strengths up to two orders of magnitude greater, but with some caveats regarding the assumptions needed and the interpretations gained from solar as well as stellar models. In our preliminary models wind mass loss does not exceed 1010 kg/s., {"references":["Folsom C. P., et al., 2016, MNRAS, 457, 580","Folsom C. P., et al., 2018, MNRAS, 474, 4956"]}

Stellar ultraviolet (UV) radiation has significant implications on habitability of their exoplanets, yet this radiation is partly unobservable due to interstellar medium absorption. We used the radiative transfer code SSRPM to build stellar models of two M dwarfs and synthesize their UV spectra, particularly focusing on the far-UV and extreme-UV spectra. Our most important findings are that 1) the coronae of two M dwarfs are responsible for more than half of their respective EUV fluxes, and 2) the continuum in the FUV band between 145 and 170 nm is responsible for about half of total emission in this band. Here, we discuss the significance of these results and outline future projects aimed to improve our understanding of solar and stellar UV emission.

Effective temperature, surface gravity, and metallicity are basic stellar parameters necessary to characterize a star. Once these parameters are obtained, we can in turn, infer their chemical abundances of various elements and in conjunction with evolutionary models to estimate their evolution, i.e., mass and radius. In this work, we use spectroscopy as a powerful tool to extract this information from stellar atmospheres applied to stars with spectral type FGK both dwarfs and giants. FASMA is a Python package to derive the main stellar atmospheric parameters based on the spectral synthesis technique. FASMA is run via terminal by setting the user options in a configuration file. FASMA includes all the inputs for spectral synthesis along with a manual for the derivation of stellar parameters and chemical abundances. The user has to provide solely the stellar spectrum for the analysis., {"references":["Tsantaki et al. (2020)","Tsantaki et al. (2018)"]}

The main objective of this work within CARMENES survey is the extraction of all available information on the chromospheric activity and its variability (rotational modulation, flares, etc.) using for that all the chromospheric indicators included in the spectral range of the spectrograph, ranging from visible (VIS), including the Na I D1, D2 He I D3, and H lines to near-infrared (NIR) that include the Ca II IRT, He I 10830 Å, Paschen a, Paschen b and Paschen d lines. We study in detail the behavior of the flux-flux relationships of lines formed at different chromosphere layers in order to a better understanding of the magnetic activity of M-type dwarf stars. For this task we have selected the CARMENES active RV-loud M Dwarfs (Tal-Or et al. 2018) and apply the spectral subtraction technique using iSTARMOD to derive te equivalent width (EW) of the chromospheric excess emission of the different lines that is converted to surface flux using the c factor methodology defined by Walkowicz et al. (2004) and implemented as Reiners & Basri (2008), using the set of BT-Settl-CIFIST [Fe/H] = 0 synthetic spectra as in Cifuentes et al. (2020). The ongoing results extends the frame of the work done for FGK stars in Martinez-Arnáiz et al. (2011) and confirms the non-universality of the flux-flux relationship presented there, with two or more distinct chromospheric emitter populations., {"references":["Barden, S. C. 1985ApJ...295..162B","Böhm-Vitense, E.  2007ApJ...657..486B","Cifuentes, C. et al.  2020A&A...642A.115C","Labarga, F. & Montes, D. 2020sea..confE.153L","López-Santiago, J., et al. 2010A&A...514A..97L","Montes et al.  1995A&A...294..165M","Montes et al.  2000A&AS..146..103M","Martinez-Arnáiz et al.  2011MNRAS.414.2629M","Quirrenbach, A., et al. 2020SPIE11447E..3CQ","Reiners, A. & Basri, G. 2008ApJ...684.1390R","Tal-Or, L. et al. 2018A&A...614A.122T","Walkowicz, L. M., et al.  2004PASP..116.1105W"]}

The magnetic phenomena on the solar surface have been the subject of several investigations over the last 400 years. The early indicator of the solar magnetic activity was the sunspot counting. The main indicators now are the International Sunspot Number, the Group Number, the Total Sunspot Area, and Photometric Sunspot Index. Several improvements in observational techniques have allowed measuring the magnetic activity using the solar/stellar spectra. The standard spectroscopic activity indicator is the S-index, based on the Ca II H&K emission lines, jointly the chromospheric component R'HK. Observations to stellar spots in other stars remain unclear, it is worth proposing a theoretical estimate to spot amount on other solar-type stars using the Sun as a star. We report a calibration between the spectroscopic chromospheric activity proxies (S-index and R'HK) and the sunspot indicators over the last decades. Our results indicate a quadratic power-law relationship.

Hydrodynamical simulations are very efficient tools to study the internal structure of stars but the wide range of time and length scales that characterize it makes it difficult to model. To cope this difficulty a common practice when modelling stellar convection is to artificially increase luminosity and thermal diffusivity by several order of magnitude. The reasons for using this artefact is for numerical stability and/or for achieving thermal relaxation We perform fully compressible 2D simulations of solar-like models using the numerical time-implicit code MUSIC. This work focuses on the impact such a practice could have on physical process like convective penetration and internal gravity waves. To do so we compare solar-like models with different enhancement factors for the luminosity and thermal diffusivity.

Gyrochronology is the study of stellar spin down with respect to age. Open clusters contain mostly homogenous stars and thus are ideal to calibrate the dependence of rotation rates on stellar mass and age. We select for this study NGC 6709, a young open cluster (∼ 150 Myr) with at least one red giant member that is similar in age to the Pleiades. We take a series of observations from May 2015 to June 2018 with the AIP’s STELLar Activity 1.2m telescope (STELLA1) and apply the point spread function to construct individual time series for 305 cluster members in our field. We search for periods within the time series utilizing four data analysis techniques: the phase dispersion minimization method, the string length method, the generalized Lomb-Scargle method, and the CLEAN method. Of the 305 cluster member stars, periods are recovered for the photometric light curves of 60 stars. We plot the Gaia colors of these stars against their periods to obtain a color-period diagram (CPD). The CPD has two main features: a sequence of slow rotators that fall along a diagonal where period increases with redder stars, and a less populated clump of rapidly rotating cool stars. The area between these two regimes is sparsely populated. We compare the results to several gyrochronology models of stellar spin down by using isochrones. The bifurcation of rotation periods is explained by the transition of stars between rapid and slow rotation as they spin down over time. The CPD of NGC 6709 is similar to those of clusters with ages around 110–160 Myrs, such as the Pleiades and NGC 2516, demonstrating consistency in stellar rotation, activity, and age across different clusters., {"references":["Amard, L., Palacios, A., Charbonnel, C., et al. 2019, , 631, A77","Cantat-Gaudin, T., Jordi, C., Vallenari, A., et al. 2018, , 618, A93","Fritzewski, D. J., Barnes, S. A., James, D. J., & Strassmeier, K. G. 2020, , 641, A51","Gaia Collaboration, Brown, A. G. A., Vallenari, A., et al. 2020, arXiv e-prints, arXiv:2012.01533","Stetson, P. B. 1987, , 99, 191"]}

Cool star atmospheres present challenges to chemical abundance studies. To date, only a handful of elements have been quantified for a handful of M dwarfs. In high-resolution spectra from the CARMENES survey, we identify a series of dramatically hyperfine-split vanadium features between 800 and 910 nm, which have strong and clean profiles throughout the early M-dwarf range. These ‘bucket-shaped’ line regions can be well-modeled with standard model atmospheres combined with the latest atomic data from VALD. From these line regions, we measure vanadium abundances for 140 nearby early M dwarfs in the CARMENES GTO sample and confirm that they follow the same trend with metallicity as the FG-type stars in the solar neighborhood, i.e., significantly above predictions from galactic chemical evolution models. Exhibiting a tight correlation with iron, vanadium abundances show promise as a potential metallicity indicator for M dwarfs. We also present evidence that several well-known chemical studies of K dwarfs have systematically overestimated their vanadium abundances largely as a result of neglecting to model hyperfine structure, a bias that worsens with decreasing temperature. Our work highlights opportunities for robust chemical analysis of cool stars afforded by high-quality spectra redward of visible.&nbsp

Solar flares are energetic explosions in the solar atmosphere, and superflares are the flares having the energy 10 - 106 times larger than that of the largest solar flare. Recently, many superflares on solar-type (G-type main-sequence; effective temperature is 5100 – 6000 K) stars were found in the initial 500 days data obtained by the Kepler spacecraft (Maehara et al. 2012; Shibayama et al. 2013). Notsu et al. (2019) conducted precise measurements and binarity check on the basis of spectroscopic observations and the Gaia-DR2 data. As a result, the number of Sun-like (effective temperature is 5600 – 6000 K and rotation period is over 20 days) superflare stars significantly decreased. We report the latest statistical analyses of superflares on solar-type stars using all of the Kepler primary mission data and Gaia-DR2 catalog. We updated the flare detection method by using highpass filter to remove rotational variations caused by starspots. We also examined the sample biases on the frequency of superflares, taking into account gyrochronology and flare detection completeness. The sample size of solar-type stars and Sun-like stars are ~4 and ~12 times, respectively, compared with Notsu et al. (2019). As a result, we found 2341 superflares on 265 solar-type stars, and 26 superflares on 15 Sun-like stars. This enabled us to have a more well-established view on the statistical properties of superflares. The observed upper limit of the flare energy decreases as the rotation period increases in solar-type stars. The frequency of superflares decreases as the stellar rotation period increases. The maximum energy we found on Sun-like stars is 4×1034 erg. Our analysis of Sun-like stars suggest that the Sun can cause superflares with energies of 7×1033 erg (~X700-class flares) and ~1×1034 erg (~X1000-class flares) once every ~3,000 years and ~6,000 years, respectively (Okamoto et al. 2021)., {"references":["Notsu, Y., Maehara, H., Honda, S., et al.\\ 2019, \\apj, 876, 58. doi:10.3847/1538-4357/ab14e6","Shibayama, T., Maehara, H., Notsu, S., et al.\\ 2013, \\apjs, 209, 5. doi:10.1088/0067-0049/209/1/5","Maehara, H., Shibayama, T., Notsu, S., et al.\\ 2012, \\nat, 485, 478. doi:10.1038/nature11063"]}

Rotation is a complex function of mass, metallicity, binarity, and age in low-mass main sequence stars. Here, we show that we can measure rotation periods from lightcurves in the TESS SCVZ and use TESS lightcurves to identify other classes of stellar variability (e.g. pulsations). However, instrument systematics prevent the detection of rotation signals longer than the TESS orbital period of 13.7 days. We use these rotation periods, rotational velocities from the APOGEE spectroscopic survey, and radii inferred from Gaia to trace rotation as a function of evolution for stars around the Kraft Break (~1.25 solar masses). Additionally, comparing the distribution of detected stars in Kepler and TESS reveals key differences between stellar populations probed by these two missions, with TESS probing a significant population of young stars that were not present in the Kepler sample., {"references":["Berger, Travis et al. (2020a). AJ, 160, 108","Berger, Travis et al. (2020b). arXiv:2001.07737","Claytor, Zachary et al. (2020). ApJ, 888, 43","Dixon, Don et al. (2020). arXiv:2005.00577","Amard, L. et al. (2020). MNRAS, 499,3481","Angus, Ruth et al. (2019). TheJournal of Open Source Software, 4, 1469","van Saders, Jennifer et al. (2016). Nature, 529, 181","van Saders, Jennifer L., & Pinsonneault, Marc H. (2013). ApJ, 776, 67","van Saders, J. L. et al. (2019). ApJ, 872, 128"]}

The spin-down of main sequence cool stars with time can be used as a tool to provide stellar ages under certain conditions. Large photometric surveys such as Kepler, TESS or even GAIA, thus relies on rotation period measurement to estimate the age of cool main sequence stars. Intriguingly, Davenport & Covey (2018) discovered a sequence of cool slower-than-expected rotators in the HR diagram suggesting a deviation from classical gyrochronology from an unknown source. This year, Amard & Matt (2020) and Claytor et al. (2020) showed that metal-rich stars are likely slower rotators on the main sequence due to being cooler and having thicker convective envelope. Using a compilation of mid-to-high resolution spectroscopic surveys of the Kepler field (LAMOST, APOGEE), we are now able to explore the effect of chemical composition on a population of rotating stars. Combined with Kepler and Gaia observations, and a grid of rotating stellar evolution model over a large range of mass and metallicity, this new sample allows us to reproduce the feature noticed by Davenport & Covey (2018) and to a later extent to explore and constrain the link between chemical composition, mass, rotation and activity., {"references":["Amard, Louis et al. (2020) associated to arXiv:2009.11785","Amard; Louis & Matt, Sean, P. (2020) associated to arXiv:2001.10404","Amard, Louis et al. (2019) associated to arXiv:1905.08516","Claytor, Zachary et al. (2020) associated to arXiv:1911.04518","Davenport, Jim & Covey, Kevin (2018) associated to arXiv:1807.09841","Reinhold, Timo et al. (2020) associated to arXiv:2005.01401","Suzuki, Takeru, K. (2018) associated to arXiv:1710.04478v2","Witzke, Veronika et al. (2020) associated to arXiv:2001.01934v1","Zhang, Jinghua et al. (2020) associated to arXiv:2005.02717"]}

This study is part of the BinaMIcS project which aims to understand the interaction between binarity and magnetism in different type of stars. Here, we present FK Aqr (GJ 867 A) – a double-line spectroscopic binary system consisting of two dM1-dwarfs with similar masses (0.55 Msun and 0.45 Msun for the primary and secondary, respectively). We were able to reconstruct the first maps of the surface magnetic field topologies of both components by employing the Zeeman Doppler imaging method. The data were obtained with ESPaDOnS spectropolarimeter at CFHT. Clear Stokes V signatures are detected from all observations of both components. The longitudinal magnetic field of the secondary is two times stronger than the primary’s one. The reconstructed maps show that both M-dwarfs have dipolar structures of their large-scale magnetic fields. This is in agreement with previous studies showing that M-dwarf stars, even in close binary pairs, can generate surface magnetic fields displaying a strong axisymmetric dipole component. We also note that the components of FK Aqr are among the most massive M-dwarfs known to generate this type of magnetic field. Orbital parameters of the system are refined employing the PHOEBE software based on the measurements of the radial velocities of both components from the mean Stokes I profiles.

We present a census of the population of local (d < 2 kpc) Galactic halo stars, based on a search of stars with large proper motions (> 40 mas/yr) from the Gaia Early Data Release 3. From this we assemble a catalog of 551,214 low-mass halo stars, for which we also derive photometric metallicity estimates. We assembled 17,803 stars as a metallicity calibration subset from various large spectroscopic surveys, such as SDSS SEGUE/APOGEE, GALAH, LAMOST, and from Hejazi et al. (2020). We expand on these results to construct a color-magnitude-metallicity grid, which can be used to estimate metallicities for all the stars using their values of MG and GRP. We find that stars in our catalog share similar kinematics as reported in recent studies of more luminous Galactic halo stars. Our sample notably shows likely new members of Gaia-Enceladus Stream of which mean photometric metallicity estimate is around -1.2 dex. We further explore how the velocity-space distribution of low-mass M stars varies with metallicity, and tentatively identify possible chemically distinct sub-populations, which could potentially be revealed in greater detail with radial velocity measurements the full Gaia Data Release 3 and from large spectroscopic surveys like SDSS-V, DESI MW survey, WEAVE, and/or 4MOST., {"references":["Ahumada, R., Allende Prieto, C., Almeida, A., et al. 2020, ApJS, 249, 3","Buder, S., Sharma, S., Kos, J., et al. 2020, arXiv:2011.02505","Gaia Collaboration, Prusti, T., de Bruijne, J. H. J., et al. 2016, A&A, 595, A1","Gaia Collaboration, Brown, A. G. A., Vallenari, A., et al. 2020, arXiv:2012.01533","Green, G. M., Schlafly, E., Zucker, C., et al. 2019, ApJ, 887, 93. doi:10.3847/1538-4357/ab5362","Hejazi, N., Lepine, S., Homeier, D., et al. 2020, AJ, 159, 30. doi:10.3847/1538-3881/ab563c","Majewski, S. R., Schiavon, R. P., Frinchaboy, P. M., et al. 2017, AJ, 154, 94","Yanny, B., Rockosi, C., Newberg, H. J., et al. 2009, AJ, 137, 4377"]}

Stellar ultraviolet (UV) radiation has significant implications on habitability of their exoplanets, yet this radiation is partly unobservable due to interstellar medium absorption. We used the radiative transfer code SSRPM to build stellar models of two M dwarfs and synthesize their UV spectra, particularly focusing on the far-UV and extreme-UV spectra. Our most important findings are that 1) the coronae of two M dwarfs are responsible for more than half of their respective EUV fluxes, and 2) the continuum in the FUV band between 145 and 170 nm is responsible for about half of total emission in this band. Here, we discuss the significance of these results and outline future projects aimed to improve our understanding of solar and stellar UV emission.

At a distance of only 1.3 pc, Proxima Cen is the closest exoplanetary system orbiting an M-type flare star, making it a benchmark case to explore the properties and potential effects of stellar activity on exoplanet atmospheres. Here, we present the discovery of an extreme flaring event from Proxima Cen by the Australian Square Kilometre Array Pathfinder (ASKAP), the Atacama Large Millimeter/submillimeter Array (ALMA), the Transiting Exoplanet Survey Satellite (TESS), the du Pont telescope at Las Campanas, and the Hubble Space Telescope (HST). In the millimeter and FUV, this flare is the brightest ever detected, brightening by a factor of >1000 and >14000 as seen by ALMA and HST, respectively. The millimeter and FUV continuum emission trace each other closely during the flare, suggesting that millimeter emission could serve as a proxy for FUV emission from stellar flares and become a powerful new tool to constrain the high-energy radiation environment of exoplanets. Optical emission is decoupled, peaking at a much lower level with a time delay. The extremely short duration of this event indicates that it could originate from a single flare loop or 'building block.' These are the first results from a larger campaign executed in April-July 2019 consisting of roughly 40 hours of simultaneous observations of Proxima Cen spanning radio to X-ray wavelengths.

Despite stellar magnetic activity being present in most cool stars, its effects on spectroscopic observations are still not well understood. Several activity indicators are routinely used to identify activity-related signals in radial velocity (RV) measurements, but not all indicators trace exactly the same effects, nor are any of them always effective in all stars. This poses one of the main obstacles for the detection and characterisation of small exoplanets, as magnetic activity biases RV signals. In this work, we analyse the temporal behaviour of RVs and a set of spectroscopic indicators for 98 M dwarfs observed with CARMENES, with the aim of finding a relation between indicator performance and stellar properties. We find periodic signals related to activity for 56 sample stars. The activity indicators behave differently depending on the mass and activity level of the target star, e.g., cross-correlation function bisector inverse slope and chromatic index are effective activity tracers for the most active stars in the sample, especially stars with relatively high mass, while for less active stars, chromospheric lines perform best. Most of the targets for which we cannot identify any activity-related signal are stars at the low-mass end of the sample, where stars are fully convective, and also show the lowest RV scatter. This could potentially hint at different manifestations of activity compared to higher-mass stars. Moreover, ultracool M dwarfs could be better candidates for planet searches than earlier types, which display higher levels of RV variability. Our results show that none of the indicators are effective activity tracers for all stars. Therefore, an analysis of a large set of indicators seems necessary to obtain a complete picture of stellar activity variability. This becomes critical when assessing the origin of RV signals, as not using the most effective indicators considering the characteristics of the star may lead to false planet claims.

The solar magnetic field is generated and sustained through an internal dynamo. In stars, this process is determined by the combined action of turbulent convective motions and the differential rotation profile. It can sometimes lead to magnetic cyclic variabilities, like in the Sun with the 11 years cycle. Traces of magnetic cycles have been detected for other stars as well, ranging from a few years to a few tens of years. How are these cycles controlled? During their life, the rotation of stars is subject to complex evolution. Recent 3D numerical simulations of solar-like stars show that different regimes of differential rotation can be characterized with the Rossby number. In particular, anti-solar differential rotation (fast poles, slow equator) may exist for a high Rossby number (slow rotators). If this regime occurs during the main sequence, and in general for slow rotators, we may wonder how the magnetic generation through dynamo process will be impacted. In particular, can slowly rotating stars have magnetic cycles? We present a numerical multi-D study with the STELEM and ASH codes to understand the magnetic field generation of solar-like stars under various differential rotation regimes, and focus on the existence of magnetic cycles. We find that short cycles are favoured for small Rossby numbers (fast rotators), and long cycles for intermediate (solar-like) Rossby numbers. Slow rotators (high Rossby numbers) are found to produce only steady dynamo with no cyclic activity in most cases considered. Magnetic cycles can be produced with anti-solar differential rotation only if the alpha effect is fine tuned for this purpose. We conclude that slow rotating stars in the anti-solar differential rotation regime can sustain magnetic cycles only for very specific dynamo processes. A detection of magnetic cycles for such stars would therefore be a tremendous constrain on deciphering what type of dynamo is actually acting in solar-like stars., A poster for the Cool Stars 20.5 Virtual Conference, {"references":["Skumanich (1972)","De Rosa, Brun et al. (2012)","Brun, Strugarek et al. (2017)"]}

We report on two state-of-the-art codes designed to characterise the spectra of late-type stars. STEPAR is a Python 3.X code that implements the EW method to calculate stellar atmospheric parameters (Teff, log(g), and [Fe/H]) of FGK stars. This code has already been extensively used to analyse high-resolution stellar spectra of thousands of Gaia-ESO Survey stars, among others. On the other hand, STEPARSYN is a Bayesian code designed to retrieve the distribution of stellar parameters of an observed spectrum using the spectral synthesis method combined with a robust scheme that rests on a Markov Chain Monte Carlo sampler.

Dark magnetic spots co-rotating with the stellar surface lead to quasi-periodic brightness variations, which enclose relevant information on stellar rotation and magnetic activity properties. In this work, we analyzed the Kepler long-cadence data of 159,710 main-sequence and subgiant FGKM stars. Rotation-period candidates are obtained by combining wavelet analysis with autocorrelation function of light curves. The final rotation periods Prot are selected via a machine learning algorithm, automatic selection, and complementary visual inspection. We successfully recover average rotation periods and photometric activity proxy Sph for 55,201 stars, which corresponds to an increase in detections of more than 60% in comparison with McQuillan et al. (2014). The rotation-period distribution is confirmed to be bimodal for the Kepler solar-type targets showing a slow- and a fast-rotating branches. While the rotation period generally decreases with increasing effective temperature Teff, the Sph behavior is more complex. For main-sequence GKM stars, Sph spans a wider range of values with increasing Teff, while F stars tend to have smaller Sph values in comparison with cooler stars. Overall, for main-sequence GKM stars, fast rotators are photometrically more active than slow rotators. For K stars, the slow- and fast-rotating branches are almost parallel in the Sph-Prot diagram, whereas for G stars the fast-rotating branch corresponds to a Sph saturated regime. Detecting Prot for a larger number of slow rotators, the upper edge of the Prot distribution is found to be located at longer periods than found previously., {"references":["Berger, T. A., et al. 2020, AJ, 159, 280","Breton, S. N., et al. 2021, arXiv:2101.10152","Ceillier, T., et al. 2017, A&A, 605, A111","Ceillier, T., et al. 2016, MNRAS, 456, 119","García, R. A., et al. 2014, A&A, 572, A34","García, R. A., et al. 2011, MNRAS, 414, L6","Jenkins, J. M., et al. 2010, ApJL, 713, L87","Mathur, S., et al. 2014, A&A, 562, A124","Mathur, S., et al. 2010, A&A, 518, A53","Mathur, S., et al. 2017, ApJS, 229, 30","McQuillan, A., et al. 2014, ApJS, 211, 24","Santos, A. R. G., et al. 2019, ApJS, 244, 21"]}

Contemporary studies of exoplanet habitability often use white-light measurements to estimate the ultraviolet (UV) effects of stellar flares, often by assuming a 9000K blackbody for the bolometric flare spectrum. We have combined TESS and archival GALEX photometry to test the UV predictions of white-light flare rates using the 9000K model and discuss the background and our methodology in this poster. We have found from our preliminary results that the UV predictions of white-light flare rates do not accurately reflect the NUV or FUV flaring activity of low-mass stars and are working to quantify the scale of this disconnect., {"references":["Venot, O., Rocchetto, M., Carl, S., et al. 2016, ApJ, 830, 77. doi:10.3847/0004-637X/830/2/77","Rimmer, P. B., Xu, J., Thompson, S. J., et al. 2018, Science Advances, 4, eaar3302. doi:10.1126/sciadv.aar3302","Gunther, M.~N., Zhan, Z., Seager, S., et al. 2020, AJ, 159, 60. doi:10.3847/1538-3881/ab5d3a","Million, C., Fleming, S.~W., Shiao, B., et al. 2016, ApJ, 833, 292. doi:10.3847/1538-4357/833/2/292"]}

The helicity of a magnetic field is a fundamental property that is conserved in ideal MHD. It can be explored in the stellar context by mapping large-scale magnetic fields across stellar surfaces using Zeeman-Doppler imaging. A recent study of 51 stars in the mass range 0.1-1.34 M$_\odot$ showed that the photospheric magnetic helicity density follows a single power law when plotted against the toroidal field energy, but splits into two branches when plotted against the poloidal field energy. These two branches divide stars above and below $\sim$ 0.5 M$_\odot$. We present here a novel method of visualising the helicity density in terms of the linkage of the toroidal and poloidal fields that are mapped across the stellar surface. This approach allows us to classify the field linkages that provide the helicity density for stars of different masses and rotation rates. We find that stars on the lower-mass branch tend to have toroidal fields that are non-axisymmetric and so link through regions of positive and negative poloidal field. A lower-mass star may have the same helicity density as a higher-mass star, despite having a stronger poloidal field. Lower-mass stars are therefore less efficient at generating large-scale helicity., Comment: 8 pages, 7 figures, 1 table

Stellar activity hinders the detection of small exoplanets with the radial velocity (RV) method, because it introduces spurious signals that can drown or mimic planetary signatures. It is therefore crucial to understand and filter out activity signals, especially in light of future small planet searches. We investigate ways to reduce activity jitter in RV time series using spectropolarimetric data sets in optical (ESPaDOnS@CHFT and NARVAL@TBL), and in near-infrared (nIR) with SPIRou@CHFT. We employ two approaches: 1) perform a chromatic study of typical stellar activity proxies, and 2) study a parametric selection of spectral lines to build a mask for Least-Square Deconvolution. The study is performed for EV Lac and AD Leo, two very active M dwarfs., {"references":["Queloz et al. 2001, A&A, 379, 279-287","Huelamo et al. 2008, A&A, 2, L9-L13","Donati et al. 1997, MNRAS, 291, 658","Boisse et al. 2009, A&A, 495, 959-966","Donati et al. 2016, Nature, 7609, 662-666","Hebrard et al. 2016, MNRAS, 461, 1465-1497","Haywood et al. 2014, MNRAS, 443, 2517-2531","Zechmeister & Kürster 2009, A&A, 496, 577-584"]}

Understanding how the magnetic activity of low-mass stars depends on their fundamental parameters is an important goal of stellar astrophysics. Previous studies suggest that the stellar mass and rotation period both play important roles in determining the overall activity level of a star. However, we currently have little information on the role of metallicity. In this poster, we study how magnetic activity scales with stellar metallicity. Specifically, we use photometric variability as a proxy for magnetic activity. Using a sample of over 3000 low-mass stars, we demonstrate that, at fixed stellar mass and rotation, more metal-rich stars are generally more magnetically active. &nbsp

In the last years efforts have been made to determine parameters of stellar coronal mass ejections (CMEs), on the one hand via acquiring dedicated observing time at telescopes and on the other hand via searching data archives. Here we present a search for CMEs on solar-like stars using optical spectroscopic data from the Polarbase and ESO HARPS Phase 3 archives. For detecting stellar CMEs we use the signature of filaments/prominences being ejected from a star, which is Doppler-shifted emission/absorption occurring on the blue side of Balmer lines, as filaments/prominences are very pronounced in Balmer lines. Using more than 3700 hours of on-source time of 425 stars we aim for a statistical determination of CME parameters, such as projected velocity, occurrence frequency, and mass. The target stars are nearby objects and consist of F-K main-sequence stars of various ages. We find no signature of CME activity and a very low level of flaring activity (10 out of 425 stars). Comparing this to results from the Kepler mission, the fraction of flaring stars is more or less consistent. Comparing extrapolated Hα flare rates to the sparse detection of flares reveals that we could have detected more flares. We therefore determined the full-disk Hα signal of one of the strongest solar flares in the last solar cycles. This showed that we would have needed data with higher S/N to detect such a flare in our data. Finally, we compared the observed upper limits of CME rates of our target stars to modelled CME rates. The modelled CME rates are mostly below the observationally determined upper limits, indicating that most on-source times per star were too short to detect stellar CMEs with this method. The sparse detection of flares and the non-detection of CMEs may be explained by biases naturally introduced by using archival data, as well as a a low level of activity of the target stars. We conclude with a short report on ongoing and future activities of the search for stellar CMEs., {"references":["Audard, M., Güdel, M., Drake, J. J., & Kashyap, V. L. 2000, ApJ, 541, 396","Balona, L. A. 2015, MNRAS, 447, 2714","Butler, C. J. 1990, in IAU Symposium, Vol. 137, Flare Stars in Star Clusters, Associations and the Solar Vicinity, ed. L. V. Mirzoian, B. R. Pettersen, & M. K. Tsvetkov, 153","Butler, C. J., Rodono, M., & Foing, B. H. 1988, A&A, 206, L1","Leitzinger, M., Odert, P., Greimel, R., et al. 2020, MNRAS, 493, 4570 [6] Moschou, S.-P., Drake, J. J., Cohen, O., et al. 2019, ApJ, 877, 105","Odert, P., Leitzinger, M., Guenther, E. W., & Heinzel, P. 2020, MNRAS, 494, 3766","Van Doorsselaere, T., Shariati, H., & Debosscher, J. 2017, ApJS, 232, 26","Yang, H. & Liu, J. 2019, ApJS, 241, 29"]}