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White-light flares are magnetically driven localized brightenings on the surfaces of stars. Their temporal, spectral, and statistical properties present a treasury of physical information about stellar magnetic fields. The spatial distributions of magnetic spots and associated flaring regions help constrain dynamo theories. Moreover, flares are thought to crucially affect the habitability of exoplanets that orbit these stars. Measuring the location of flares on stars other than the Sun is challenging due to the lack of spatial resolution. Here we present four fully convective stars observed with the Transiting Exoplanet Survey Satellite (TESS) that displayed large, long-duration flares in white-light which were modulated in brightness by the stars' fast rotation. This allowed us to determine the loci of these flares directly from the light curves. All four flares occurred at latitudes between 55 deg and 81 deg, far higher than typical solar flare latitudes. Our findings are evidence that strong magnetic fields tend to emerge close to the stellar rotational poles for fully convective stars, and suggest that the impact of flares on the habitability of exoplanets around small stars could be weaker than previously thought., Comment: 23 pages, 18 figures, accepted to MNRAS, see conference poster https://doi.org/10.5281/zenodo.4558791 for short summary

Star spot evolution is visible evidence of the emergence/decay of the magnetic field on stellar surface, and it is therefore important for the understanding of the underlying stellar dynamo and consequential stellar flares. In this paper, we report the temporal evolution of individual star spot area on the hot-Jupiter-hosting active solar-type star Kepler 17 whose transits occur every 1.5 days. The spot longitude and area evolution are estimated (1) from the stellar rotational modulations of Kepler data and (2) from the brightness enhancements during the exoplanet transits caused by existence of large star spots. As a result of the comparison, number of spots, spot locations, and the temporal evolution derived from the rotational modulations is largely different from those of in-transit spots. We confirm that although only two light curve minima appear per rotation, there are clearly many spots present on the star. We find that the observed differential intensity changes are sometimes consistent with the spot pattern detected by transits, but they sometimes do not match with each other. Although the temporal evolution derived from the rotational modulation differs from those of in-transit spots to a certain degree, the emergence/decay rates of in-transit spots are within an order of magnitude of those derived for sunspots as well as our previous research based only on rotational modulations. This supports a hypothesis that the emergence/decay of sunspots and extremely-large star spots on solar-type stars occur through the same underlying processes., Comment: 37 pages, 12 figures, 1 table. Accepted for publication in The Astrophysical Journal

The flaring M4 dwarf GJ 1243 has become a benchmark for studying stellar flare and starspot activity thanks to the exceptional photometric monitoring archive from the Kepler mission. New light curves from the TESS mission for this star allow precise stellar activity characterization over more than a decade timescale. We have carried out the first flare and starspot analysis of GJ 1243 from over 50 days of data from TESS Sectors 14 and 15. Using 133 flare events detected in the 2-minute cadence TESS data, we compare the cumulative flare frequency distributions, and find the flare activity for GJ 1243 is unchanged between the Kepler and TESS epochs. Two distinct starspot groups are found in the TESS data, with the primary spot having the same rotational period and phase as seen in Kepler. The phase of the secondary spot feature is consistent with the predicted location of the secondary starspot and measurement of weak differential rotation, suggesting this secondary spot may be long-lived and stable in both latitude and longitude. As expected for this highly active star, the constant spot and flare activity reveal no sign of solar-like activity cycles over 10 years. However, we highlight the unique ability for Kepler and TESS to use flare rates to detect activity cycles., Comment: 14 pages, 5 figures, AJ accepted

We examine how tides, stellar evolution, and magnetic braking shape the rotation period (P$_{rot}$) evolution of low-mass stellar binaries up to orbital periods (P$_{orb}$) of 100 d across a wide range tidal dissipation parameters using two common equilibrium tidal models. We find that many binaries with P$_{orb} < 20$ d tidally lock, and most with $P_{orb} < 4$ d tidally lock into synchronous rotation on circularized orbits. At short P$_{orb}$, tidal torques produce a population of fast rotators that single-star only models of magnetic braking fail to produce. In many cases, we show that the competition between magnetic braking and tides produces a population of subsynchronous rotators that persists for Gyrs, even in short P$_{orb}$ binaries, qualitatively reproducing the subsynchronous eclipsing binaries (EBs) discovered in the Kepler field by Lurie et al. (2017). Both equilibrium tidal models predict that binaries can tidally-interact out to P$_{orb} \approx 80$ d, while the Constant Phase Lag tidal model predicts that binaries can tidally lock out to P$_{orb} \approx 100$ d. Tidal torques often force the P$_{rot}$ evolution of stellar binaries to depart from the long-term magnetic braking-driven spin down experienced by single stars, revealing that P$_{rot}$ is not be a valid proxy for age in all cases, i.e. gyrochronology can underpredict ages by up to $300\%$ unless one accounts for binarity. We suggest that accurate determinations of orbital eccentricties and P$_{rot}$ can be used to discriminate between which equilibrium tidal models best describes tidal interactions in low-mass binary stars., Accepted, ApJ

Using a recent census of flare stars from the Kepler survey, we have explored how flare activity evolves across stellar main sequence lifetimes. We utilize a sample of 347 stars with robust flare activity detections, and which have rotation periods measured via starspot modulations in their Kepler light curves. We consider three separate methods for quantifying flare activity from optical light curves, and compare their utility for comparing flare activity between stars of differing ages and luminosities. These metrics include: the fractional luminosity emitted in flares, the specific rate of flares emitted at a given energy, and a model for the entire flare frequency distribution. With all three approaches we find that flare activity decreases for all low-mass stars as they spin-down, and thus with age. Most striking is the evolution of the flare occurrence frequency distributions, which show no significant change in the power law slope with age. Since our sample is preferentially constructed of younger, more active stars, our model over-predicts the super-flare rate previously estimated for the Sun. Finally, we parameterize our best-fit model of the flare frequency distribution for ease in predicting the rates of flares and their associated impacts on planet habitability and detection., Comment: 21 pages, 11 figures, ApJ Accepted 2018-Dec-31

In the coming years, next-generation space-based infrared observatories will significantly increase our samples of rare massive stars, representing a tremendous opportunity to leverage modern statistical tools and methods to test massive stellar evolution in entirely new environments. Such work is only possible if the observed objects can be reliably classified. Spectroscopic observations are infeasible with more distant targets, and so we wish to determine whether machine learning methods can classify massive stars using broadband infrared photometry. We find that a Support Vector Machine classifier is capable of coarsely classifying massive stars with labels corresponding to hot, cool, and emission line stars with high accuracy, while rejecting contaminating low mass giants. Remarkably, 76\% of emission line stars can be recovered without the need for narrowband or spectroscopic observations. We classify a sample of ${\sim}2500$ objects with no existing labels, and identify fourteen candidate emission line objects. Unfortunately, despite the high precision of the photometry in our sample, the heterogeneous origins of the labels for the stars in our sample severely inhibits our classifier from distinguishing classes of stars with more granularity. Ultimately, no large and homogeneously labeled sample of massive stars currently exists. Without significant efforts to robustly classify evolved massive stars -- which is feasible given existing data from large all-sky spectroscopic surveys -- shortcomings in the labeling of existing data sets will hinder efforts to leverage the next-generation of space observatories., 23 pages, 16 figures, 6 tables. Accepted for publication in ApJ. Comments welcome

Flares, energetic eruptions on the surfaces of stars, are an unmistakable manifestation of magnetically driven emission. Their occurrence rates and energy distributions trace stellar characteristics such as mass and age. But before flares can be used to constrain stellar properties, the flaring-age-mass relation requires proper calibration. This work sets out to quantify flaring activity of independently age-dated main sequence stars for a broad range of spectral types using optical light curves obtained by the Kepler satellite. Drawing from the complete K2 archive, we searched 3435 $\sim 80$ day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates. We confirmed a total of 3844 flares on high probability open cluster members with ages from zero age main sequence (Pleiades) to 3.6 Gyr (M67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-M dwarfs. We added the Hyades (690 Myr) to the sample as a comparison cluster to Praesepe (750 Myr), the 2.6 Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. The flare energy distribution was similar in the entire parameter space, following a power law relation with exponent $\alpha\approx 1.84-2.39$. The flaring rates declined with age, and declined faster for higher mass stars. We found evidence that a rapid decline in flaring activity occurred in M1-M2 dwarfs around Hyades/Praesepe age, when these stars spun down to rotation periods of about 10 days, while higher mass stars had already transitioned to lower flaring rates, and lower mass stars still resided in the saturated activity regime. (abridged), Comment: 27 pages, 13 figures. Accepted to A&A

Zeeman Doppler Imaging (ZDI) is a powerful tool for characterizing the strength and topology of stellar magnetic fields. In this research note, we present a new way to visualize the typical results from ZDI for an ensemble of stars, addressing some of the concerns with the standard "confusogram" approach to illustrating the data. Our publicly available plotting methods further enable an accessible means to consider variability in the inferred magnetic field topologies from repeated observations, as we demonstrate with the literature ZDI data on M dwarfs.

We observed eclipses of the transiting brown dwarf CWW 89Ab at 3.6um and 4.5um using Spitzer/IRAC. The CWW 89 binary system is a member of the $3.0\pm0.25$ Gyr-old open cluster Ruprecht 147, and is composed of a Sun-like primary and an early M-dwarf secondary separated by a projected distance of 25 AU. CWW 89Ab has a radius of $0.937\pm0.042$ RJ and a mass of $36.5\pm0.1$ MJ, and is on a 5.3 day orbit about CWW 89A with a non-zero eccentricity of $e=0.19$ (Curtis et al. 2016). We strongly detect the eclipses of CWW 89Ab in both Spitzer channels as $\delta_{3.6}=1147\pm213$ ppm and $\delta_{4.5}=1097\pm225$ ppm after correcting for the dilution from CWW 89B. After accounting for the irradiation that CWW 89Ab receives from its host star, these measurements imply that the brown dwarf has an internal luminosity of $\log(\mathrm{L_{bol}/\mathrm{L}_\odot})=-4.19\pm0.14$. This is 16 times, or $9.3\,\sigma$, higher than model predictions given the known mass, radius, and age of CWW 89Ab. As we discuss, this over-luminosity is not explainable by an inaccurate age determination, additional stellar heating, nor tidal heating. Instead, we suggest that the anomalous luminosity of CWW 89Ab is caused by a dayside temperature inversion -- though a significant error in the evolutionary models is also a possibility. Importantly, a temperature inversion would require a super-stellar C/O ratio in CWW 89Ab's atmosphere. If this is indeed the case, it implies that CWW 89Ab is a 36.5 MJ object that formed via core accretion processes. Finally, we use our measurement of CWW 89Ab's orbital eccentricity, improved via these observations, to constrain the tidal quality factors of the brown dwarf and the host star CWW 89A to be $Q_{BD}>10^{4.15}$ and $Q_*>10^{9}$, respectively., Comment: 19 pages, 12 figures. AJ in press. Updated based on comments received

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <, 19 pages, 8 figures, accepted for publication in ApJL

Over the last decade, significant attention has been drawn to the gender ratio of speakers at conferences, and many meetings are evolving to better reflect the gender balance of the field as a whole. We find that women are significantly under-represented, however, among the astronomers asking questions after talks., Comment: Nature Astronomy Comment from June 2017. Final version available at Nature Astronomy (https://www.nature.com/articles/s41550-017-0153 web) or (http://rdcu.be/tb3q pdf)

The enigmatic star KIC 8462852, informally known as "Boyajian's Star", has exhibited unexplained variability from both short timescale (days) dimming events, and years-long fading in the Kepler mission. No single physical mechanism has successfully explained these observations to date. Here we investigate the ultraviolet variability of KIC 8462852 on a range of timescales using data from the GALEX mission that occurred contemporaneously with the Kepler mission. The wide wavelength baseline between the Kepler and GALEX data provides a unique constraint on the nature of the variability. Using 1600 seconds of photon-counting data from four GALEX visits spread over 70 days in 2011, we find no coherent NUV variability in the system on 10-100 second or months timescales. Comparing the integrated flux from these 2011 visits to the 2012 NUV flux published in the GALEX-CAUSE Kepler survey, we find a 3% decrease in brightness for KIC 8462852. We find this level of variability is significant, but not necessarily unusual for stars of similar spectral type in the GALEX data. This decrease coincides with the secular optical fading reported by Montet & Simon (2016). We find the multi-wavelength variability is somewhat inconsistent with typical interstellar dust absorption, but instead favors a R$_V$ = 5.0 $\pm$ 0.9 reddening law potentially from circumstellar dust., 8 pages, 4 figures, ApJ Accepted

Kepler photometry of the hot Neptune host star HAT-P-11 suggests that its spot latitude distribution is comparable to the Sun's near solar maximum. We search for evidence of an activity cycle in the CaII H & K chromospheric emission $S$-index with archival Keck/HIRES spectra and observations from the echelle spectrograph on the ARC 3.5 m Telescope at APO. The chromospheric emission of HAT-P-11 is consistent with a $\gtrsim 10$ year activity cycle, which plateaued near maximum during the Kepler mission. In the cycle that we observed, the star seemed to spend more time near active maximum than minimum. We compare the $\log R^\prime_{HK}$ normalized chromospheric emission index of HAT-P-11 with other stars. HAT-P-11 has unusually strong chromospheric emission compared to planet-hosting stars of similar effective temperature and rotation period, perhaps due to tides raised by its planet., 16 pages, 8 figures; accepted to the Astrophysical Journal

We identify a sample of near-equal mass wide binary M dwarf systems from the SLoWPoKES catalog of common proper-motion binaries and obtain follow-up observations of their chromospheric activity as measured by the Hα emission line. We present optical spectra for both components of 48 candidate M dwarf binaries, confirming their mid-M spectral types. Of those 48 coeval pairs, we find eight with Hα emission from both components, three with weak emission in one component and no emission in the other, and 37 with two inactive components. We find that of the 11 pairs with at least one active component, only three follow the net trend of decreasing activity strength (LHα/Lbol) with later spectral type. The difference in quiescent activity strength between the A and B components is larger than what would be expected based on the small differences in color (mass). For five binaries with two active components, we present 47 hr of time-resolved spectroscopy, observed on the ARC 3.5-m over 12 different nights. For four of the five pairs, the slightly redder (B) component exhibits a higher level of Hα emission during the majority of the observations and the redder objects are the only components to flare. The full range of Hα emission observed on these variable mid-M dwarfs is comparable to the scatter in Hα emission found in single-epoch surveys of mid-M dwarfs, indicating that variability could be a major factor in the spread of observed activity strengths. We also find that variability is independent of both activity strength and spectral type.

We present the fiducial main sequence stellar locus traced by 10 photometric colors observed by SDSS, 2MASS, and WISE. Median colors are determined using 1,052,793 stars with rband extinction less than 0.125. We use this locus to measure the dust extinction curve relative to the r-band, which is consistent with previous measurements in the SDSS and 2MASS bands. The WISE band extinction coefficients are larger than predicted by standard extinction models. Using 13 lines of sight, we find variations in the extinction curve in H, Ks, and WISE bandpasses. Relative extinction decreases towards Galactic anti-center, in agreement with prior studies. Relative extinction increases with Galactic latitude, in contrast to previous observations. This indicates a universal mid-IR extinction law does not exist due to variations in dust grain size and chemistry with Galactocentric position. A preliminary search for outliers due to warm circumstellar dust is also presented, using stars with high signal-to-noise in the W3-band. We find 199 such outliers, identified by excess emission in Ks W3. Inspection of SDSS images for these outliers reveals a large number of contaminants due to nearby galaxies. Six sources appear to be genuine dust candidates, yielding a fraction of systems with infrared excess of 0:12 0:05%.

Quasi-periodic pulsations (QPPs) appear to be a common feature observed in the light curves of both solar and stellar flares. However, their quasi-periodic nature, along with the fact that they can be small in amplitude and short-lived, makes QPPs difficult to unequivocally detect. In this paper, we test the strengths and limitations of state-of-the-art methods for detecting QPPs using a series of hare-and-hounds exercises. The hare simulated a set of flares, both with and without QPPs of a variety of forms, while the hounds attempted to detect QPPs in blind tests. We use the results of these exercises to create a blueprint for anyone who wishes to detect QPPs in real solar and stellar data. We present eight clear recommendations to be kept in mind for future QPP detections, with the plethora of solar and stellar flare data from new and future satellites. These recommendations address the key pitfalls in QPP detection, including detrending, trimming data, accounting for colored noise, detecting stationary-period QPPs, detecting QPPs with nonstationary periods, and ensuring that detections are robust and false detections are minimized. We find that QPPs can be detected reliably and robustly by a variety of methods, which are clearly identified and described, if the appropriate care and due diligence are taken., Accepted for publication in ApJSS, 46 pages, 29 figures, 7 tables

The presence and strength of a stellar magnetic field and activity is rooted in a star's fundamental parameters such as mass and age. Can flares serve as an accurate stellar "clock"? To explore if we can quantify an activity-age relation in the form of a flaring-age relation, we measured trends in the flaring rates and energies for stars with different masses and ages. We investigated the time-domain photometry provided by Kepler's follow-up mission K2 and searched for flares in three solar metallicity open clusters with well-known ages, M45 (0.125 Gyr), M44 (0.63 Gyr), and M67 (4.3 Gyr). We updated and employed the automated flare finding and analysis pipeline Appaloosa, originally designed for Kepler. We introduced a synthetic flare injection and recovery subroutine to ascribe detection and energy recovery rates for flares in a broad energy range for each light curve. We collected a sample of 1 761 stars, mostly late-K to mid-M dwarfs and found 751 flare candidates with energies ranging from $4\cdot10^{32}$ erg to $6\cdot10^{34}$ erg, of which 596 belong to M45, 155 to M44, and none to M67. We find that flaring activity depends both on $T_\mathrm{eff}$, and age. But all flare frequency distributions have similar slopes with $\alpha \approx2.0-2.4$, supporting a universal flare generation process. We discuss implications for the physical conditions under which flares occur, and how the sample's metallicity and multiplicity affect our results., Comment: 17 pages, 11 figures, appendix. Accepted to A&A

We present a study of white light flares from the active M5.5 dwarf Proxima Centauri using the Canadian microsatellite MOST. Using 37.6 days of monitoring data from 2014 and 2015, we have detected 66 individual flare events, the largest number of white light flares observed to date on Proxima Cen. Flare energies in our sample range from $10^{29}$-$10^{31.5}$ erg. The flare rate is lower than that of other classic flare stars of similar spectral type, such as UV Ceti, which may indicate Proxima Cen had a higher flare rate in its youth. Proxima Cen does have an unusually high flare rate given its slow rotation period, however. Extending the observed power-law occurrence distribution down to $10^{28}$ erg, we show that flares with flux amplitudes of 0.5% occur 63 times per day, while superflares with energies of $10^{33}$ erg occur ~8 times per year. Small flares may therefore pose a great difficulty in searches for transits from the recently announced 1.27 M_earth Proxima b, while frequent large flares could have significant impact on the planetary atmosphere., Comment: 6 pages, 4 figures, ApJ Letters accepted

Astrometric data from the recent Gaia Data Release 1 has been matched against the sample of stars from Kepler with known rotation periods. A total of 1,299 bright rotating stars were recovered from the subset of Gaia sources with good astrometric solutions, most with temperatures hotter than 5000 K. From these sources, 894 were selected as lying near the main sequence using their absolute G-band magnitudes. These main sequence stars show a bimodality in their rotation period distribution, centered roughly around a 600 Myr rotation-isochrone. This feature matches the bimodal period distribution found in cooler stars with Kepler, but was previously undetected for solar-type stars due to sample contamination by subgiants. A tenuous connection between the rotation period and total proper motion is found, suggesting the period bimodality is due to the age distribution of stars within ~300pc of the Sun, rather than a phase of rapid angular momentum loss. This work emphasizes the unique power for understanding stellar populations by combining temporal monitoring from Kepler with astrometric data from Gaia., Comment: 6 pages, 5 figures, ApJ Accepted. Written as part of the 2016 NYC Gaia Sprint

We present the effective temperatures ($T_{\rm eff}$), metallicities, and colours in SDSS, 2MASS, and WISE filters, of a sample of 3834 late-K and early-M dwarfs selected from the Sloan Digital Sky Survey APOGEE spectroscopic survey ASPCAP catalog. We confirm that ASPCAP $T_{\rm eff}$ values between 3550 K$, Comment: 14 pages, 6 tables, 5 figures, accepted for publication in MNRAS

We use ~12,000 spectra of ~3500 magnetically active M0-M9 dwarfs from the Sloan Digital Sky Survey taken at 10-15 minute intervals, together with ~300 spectra of ~60 M0-M8 stars obtained hourly with the Hydra multiobject spectrometer, to probe Hα variability on timescales of minutes to weeks. With multiple observations for every star examined, we are able to characterize fluctuations in Hα emission as a function of activity strength and spectral type. Stars with greater magnetic activity (as quantified by LHα/Lbol) are found to be less variable at all spectral types. We attribute this result to the stronger level of persistent emission in the high-activity stars, requiring a larger heating event in order to produce measurable variability. We also construct Hα structure functions to constrain the timescale of variability. The more active objects with lower variability exhibit a characteristic timescale longer than 1 hr, likely due to larger, longer lasting heating events, while the less active objects with higher variability have a characteristic timescale shorter than 15 minutes.

We have matched the astrometric data from Gaia Data Release 2 to the sample of stars with measured rotation periods from Kepler. Using 30,305 stars with good distance estimates, we select 16,248 as being likely main sequence single stars centered within a 0.5 mag region about a 1 Gyr isochrone, removing many sub-giants and unresolved binary stars from the sample. The rotation period bimodality, originally discovered by McQuillan et al. (2013), is clearly recovered for stars out to 525pc, but is not detectable at further distances. This bimodality correlates with Galactic height as well, dropping strongly for stars above Z>90 pc. We also find a significant width in the stellar main sequence of $\Delta M_G$ ~0.25 mag, as well as a coherent gradient of increasing rotation periods orthogonal to the main sequence. We interpret this as a signature of stellar angular momentum loss over time, implying a corresponding diagonal age gradient across the main sequence. Stellar evolution models predict changes in color and luminosity that are consistent in amplitude, but not in direction, with those required to produce the gradient we have detected. This rotation gradient suggests that main sequence evolution produces offsets in color-magnitude space that are significantly more orthogonal to the zero-age main sequence than models currently predict, and may provide new tests for both stellar evolution and gyrochronology models., Comment: ApJ Submitted

We probe the spatial and dynamical structure of the old open cluster M67 using photometric data from the Sloan Digital Sky Survey's sixth data release. Making use of an optimal contrast, or matched filter, algorithm, we map the distribution of high probability members of M67. We find an extended and elongated halo of likely members to a radius of nearly 60'. Our measured core radius of Rcore = 8.'24+/-0.'60 is somewhat larger than that of previous estimates. We attribute the larger core radius measurement to the SDSS probing lower mass main sequence stars than has been done before for similar studies of M67, and the exclusion of post main sequence M67 members in the SDSS sample. We estimate the number of M67 members in our SDSS sample to be 1385+/-67 stars. A lower limit on the binary fraction in M67 is measured to be 45%. A higher fraction of binary stars is measured in the core as compared to the halo, and the luminosity function of the core is found to be more depleted of low-mass stars. Thus the halo is consistent with mass segregation within the cluster. The galactic orbit of M67 is calculated from recent proper motion and radial velocity determinations. The elongated halo is roughly aligned to the proper motion of the cluster. This appears to be a result of mass segregation due to the galactic tidal field. Our algorithm is run on 2MASS photometry to directly compare to previous studies of M67. Decreasing core radii are found for stars with greater masses. We test the accuracy of our algorithm using 1000 artificial cluster Monte Carlo simulations. It is found that the matched filter technique is suitable for recovering low-density spatial structures, as well as measuring the binary fraction of the cluster.

We present an analysis of flare activity in wide binary stars using a combination of value-added data sets from the NASA Kepler mission. The target list contains a set of previously discovered wide binary star systems identified by proper motions in the Kepler field. We cross-matched these systems with estimates of flare activity for $\sim$200,000 stars in the Kepler field, allowing us to compare relative flare luminosity between stars in coeval binaries. From a sample of 184 previously known wide binaries in the Kepler field, we find 58 with detectable flare activity in at least 1 component, 33 of which are similar in mass (q $>$ 0.8). Of these 33 equal-mass binaries, the majority display similar ($\pm 1$ dex) flare luminosity between both stars, as expected for stars of equal mass and age. However, we find two equal-mass pairs where the secondary (lower mass) star is more active than its counterpart, and two equal-mass pairs where the primary star is more active. The stellar rotation periods are also anomalously fast for stars with elevated flare activity. Pairs with discrepant rotation and activity qualitatively seem to have lower mass ratios. These outliers may be due to tidal spin-up, indicating these wide binaries could be hierarchical triple systems. We additionally present high resolution adaptive optics images for two wide binary systems to test this hypothesis. The demographics of stellar rotation and magnetic activity between stars in wide binaries may be useful indicators for discerning formation scenarios of these systems., 15 pages, 10 figures, accepted by ApJ

This paper describes the Seventh Data Release of the Sloan Digital Sky Survey (SDSS), marking the completion of the original goals of the SDSS and the end of the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most of the roughly 2000 deg^2 increment over the previous data release lying in regions of low Galactic latitude. The catalog contains five-band photometry for 357 million distinct objects. The survey also includes repeat photometry over 250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A coaddition of these data goes roughly two magnitudes fainter than the main survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2 in the Northern Galactic Cap, closing the gap that was present in previous data releases. There are over 1.6 million spectra in total, including 930,000 galaxies, 120,000 quasars, and 460,000 stars. The data release includes improved stellar photometry at low Galactic latitude. The astrometry has all been recalibrated with the second version of the USNO CCD Astrograph Catalog (UCAC-2), reducing the rms statistical errors at the bright end to 45 milli-arcseconds per coordinate. A systematic error in bright galaxy photometr is less severe than previously reported for the majority of galaxies. Finally, we describe a series of improvements to the spectroscopic reductions, including better flat-fielding and improved wavelength calibration at the blue end, better processing of objects with extremely strong narrow emission lines, and an improved determination of stellar metallicities. (Abridged), Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor corrections

Active galactic nuclei (AGNs) are well-known to exhibit flux variability across a wide range of wavelength regimes, but the precise origin of the variability at different wavelengths remains unclear. To investigate the relatively unexplored near-IR variability of the most luminous AGNs, we conduct a search for variability using well sampled JHKs-band light curves from the 2MASS survey calibration fields. Our sample includes 27 known quasars with an average of 924 epochs of observation over three years, as well as one spectroscopically confirmed blazar (SDSSJ14584479+3720215) with 1972 epochs of data. This is the best-sampled NIR photometric blazar light curve to date, and it exhibits correlated, stochastic variability that we characterize with continuous auto-regressive moving average (CARMA) models. None of the other 26 known quasars had detectable variability in the 2MASS bands above the photometric uncertainty. A blind search of the 2MASS calibration field light curves for AGN candidates based on fitting CARMA(1,0) models (damped-random walk) uncovered only 7 candidates. All 7 were young stellar objects within the {\rho} Ophiuchus star forming region, five with previous X-ray detections. A significant {\gamma}-ray detection (5{\sigma}) for the known blazar using 4.5 years of Fermi photon data is also found. We suggest that strong NIR variability of blazars, such as seen for SDSSJ14584479+3720215, can be used as an efficient method of identifying previously-unidentified {\gamma}-ray blazars, with low contamination from other AGN., Comment: 6 pages, 3 figures, ApJ Accepted

Ultra-precise light curves from Kepler provide the best opportunity to determine rates and statistical properties of stellar flares. From 11 months of data on the active M4 dwarf, GJ 1243, we have built the largest catalog of flares for a single star: over 6100 events. Combining 885 of our most pristine flares, we generated an empirical white-light flare template. This high-fidelity template shows a rapid initial rise, and two distinct exponential cooling phases. This template is useful in constraining flare energies and for improved flare detection in many surveys. Complex, multi-peaked events are more common for higher energy flares in this sample. Using our flare template we characterize the structure of complex events. In this contributed talk, I presented results from our boutique study of GJ 1243, and described an expanded investigation of the structure of complex flares and their connection to solar events., Comment: 6 pages, 6 figures, to appear in the Proceedings of "Solar and Stellar Flares and their Effects on Planets Proceedings", IAU Symposium No. 320, 2015. Flare sample is available online http://github.com/jradavenport/GJ1243-Flares

The SDSS III APOGEE survey recently identified two new $\sigma$ Ori E type candidates, HD 345439 and HD 23478, which are a rare subset of rapidly rotating massive stars whose large (kGauss) magnetic fields confine circumstellar material around these systems. Our analysis of multi-epoch photometric observations of HD 345439 from the KELT, SuperWASP, and ASAS surveys reveals the presence of a $\sim$0.7701 day period in each dataset, suggesting the system is amongst the faster known $\sigma$ Ori E analogs. We also see clear evidence that the strength of H-alpha, H I Brackett series lines, and He I lines also vary on a $\sim$0.7701 day period from our analysis of multi-epoch, multi-wavelength spectroscopic monitoring of the system from the APO 3.5m telescope. We trace the evolution of select emission line profiles in the system, and observe coherent line profile variability in both optical and infrared H I lines, as expected for rigidly rotating magnetosphere stars. We also analyze the evolution of the H I Br-11 line strength and line profile in multi-epoch observations of HD 23478 from the SDSS-III APOGEE instrument. The observed periodic behavior is consistent with that recently reported by Sikora and collaborators in optical spectra., Comment: Accepted in ApJL

Few observational constraints exist for the tidal synchronization rate of late-type stars, despite its fundamental role in binary evolution. We visually inspected the light curves of 2278 eclipsing binaries (EBs) from the Kepler Eclipsing Binary Catalog to identify those with starspot modulations, as well as other types of out-of-eclipse variability. We report rotation periods for 816 EBs with starspot modulations, and find that 79% of EBs with orbital periods less than ten days are synchronized. However, a population of short period EBs exists with rotation periods typically 13% slower than synchronous, which we attribute to the differential rotation of high latitude starspots. At 10 days, there is a transition from predominantly circular, synchronized EBs to predominantly eccentric, pseudosynchronized EBs. This transition period is in good agreement with the predicted and observed circularization period for Milky Way field binaries. At orbital periods greater than about 30 days, the amount of tidal synchronization decreases. We also report 12 previously unidentified candidate $\delta$ Scuti and $\gamma$ Doradus pulsators, as well as a candidate RS CVn system with an evolved primary that exhibits starspot occultations. For short period contact binaries, we observe a period-color relation, and compare it to previous studies. As a whole, these results represent the largest homogeneous study of tidal synchronization of late-type stars., Comment: Accepted for publication in the Astronomical Journal. EB rotation periods and classifications available at https://github.com/jlurie/decatur/blob/master/decatur/data/final_catalog.csv

Many current and future exoplanet missions are pushing to infrared (IR) wavelengths where the flux contrast between the planet and star is more favorable (Deming et al. 2009), and the impact of stellar magnetic activity is decreased. Indeed, a recent analysis of starspots and faculae found these forms of stellar activity do not substantially impact the transit signatures or science potential for FGKM stars with JWST (Zellem et al. 2017). However, this is not true in the case of flares, which I demonstrate can be a hinderance to transit studies in this note.

We measure the starspot radii and latitude distribution on the K4 dwarf HAT-P-11 from Kepler short-cadence photometry. We take advantage of starspot occultations by its highly-misaligned planet to compare the spot size and latitude distributions to those of sunspots. We find that the spots of HAT-P-11 are distributed in latitude much like sunspots near solar activity maximum, with mean spot latitude of $16 \pm 1$ degrees. The majority of starspots of HAT-P-11 have physical sizes that closely resemble the sizes of sunspots at solar maximum. We estimate the mean spotted area coverage on HAT-P-11 is $3^{+6}_{-1}\%$, roughly two orders of magnitude greater than the typical solar spotted area., Comment: 28 pages, 16 figures, accepted for publication in the Astrophysical Journal (August 7, 2017)

We present a comprehensive study of the active dM4e star GJ 1243. We use previous observations and ground-based echelle spectroscopy to determine that GJ 1243 is a member of the Argus association of field stars, suggesting it is $\sim 30-50$ Myr old. We analyze eleven months of 1-minute cadence data from Kepler, presenting Kepler flare frequency distributions, as well as determining correlations between flare energy, amplitude, duration, and decay time. We find that the exponent $\alpha$ of the power-law flare energy distribution varies in time, primarily due to completeness of sample and the low frequency of high-energy flares. We also find a deviation from a single power law at high energy. We use ground-based spectroscopic observations simultaneous with the Kepler data to provide simultaneous photometric and spectroscopic analysis of three low-energy flares, the lowest-energy dMe flares with detailed spectral analysis to date on any star. The spectroscopic data from these flares extend constraints for radiative hydrodynamic (RHD) flare models to a lower energy regime than has previously been studied. We use this simultaneous spectroscopy and Kepler photometry to develop approximate conversions from the \textit{Kepler} bandpass to the traditional $U$ and $B$ bands. This conversion will be a critical factor in comparing any Kepler flare analyses to the canon of previous ground-based flare studies., Comment: 13 pages, 12 figures, accepted for publication in ApJ

Selecting astrometric and photometric data from the Sloan Digital Sky Survey (SDSS), the Lepine & Shara Proper Motion North Catalog (LSPM‐North), the Two Micron All Sky Survey (2MASS), and the USNO‐B catalog, we explore a succession of methods to isolate white dwarf (WD) candidates for followup spectroscopy. Our preliminary methods include: reduced proper motion diagram cuts, color cuts, and atmospheric model adherence. After initial spectroscopic observations with the CTIO 4m Blanco telescope, we realized high subdwarf (SD) contamination solely in the cool WD temperature regime (Teff

We present measurements of the luminosity and mass functions of low-mass stars constructed from a catalog of matched Sloan Digital Sky Survey (SDSS) and 2 Micron All Sky Survey (2MASS) detections. This photometric catalog contains more than 25,000 matched SDSS and 2MASS point sources spanning ~30 square degrees on the sky. We have obtained follow-up spectroscopy, complete to J=16, of more than 500 low mass dwarf candidates within a 1 square degree sub-sample, and thousands of additional dwarf candidates in the remaining 29 square degrees. This spectroscopic sample verifies that the photometric sample is complete, uncontaminated, and unbiased at the 99% level globally, and at the 95% level in each color range. We use this sample to derive the luminosity and mass functions of low-mass stars over nearly a decade in mass (0.7 M_sun > M_* > 0.1 M_sun). We find that the logarithmically binned mass function is best fit with an M_c=0.29 log-normal distribution, with a 90% confidence interval of M_c=0.20--0.50. These 90% confidence intervals correspond to linearly binned mass functions peaking between 0.27 M_sun and 0.12 M_sun, where the best fit MF turns over at 0.17 M_sun. A power law fit to the entire mass range sampled here, however, returns a best fit of alpha=1.1 (where the Salpeter slope is alpha = 2.35). These results agree well with most previous investigations, though differences in the analytic formalisms adopted to describe those mass functions can give the false impression of disagreement. Given the richness of modern-day astronomical datasets, we are entering the regime whereby stronger conclusions can be drawn by comparing the actual datapoints measured in different mass functions, rather than the results of analytic analyses that impose structure on the data a priori. (abridged), Accepted for publication in the Astronomical Journal. 21 pages, emulateapj format, 12 figures. Figures 1, 4, 11 and 12 degraded for astroph; full resolution version available for download at http://www.cfa.harvard.edu/~kcovey/

We present a new set of photometric transformations for red stars observed with the Sloan Digital Sky Survey (SDSS) 0.5-m Photometric Telescope (PT) and the SDSS 2.5-m telescope at the Apache Point Observatory in New Mexico. Nightly PT observations of US Naval Observatory standards are used to determine extinction corrections and calibration terms for SDSS 2.5-m photometry. Systematic differences between the PT and native SDSS 2.5-m {\it ugriz} photometry require conversions between the two systems which have previously been undefined for the reddest stars. By matching $\sim 43,000$ stars observed with both the PT and SDSS 2.5-m, we extend the present relations to include low-mass stars with colors $0.6 \le r-i \le 1.7$. These corrections will allow us to place photometry of bright, low-mass trigonometric parallax stars previously observed with the PT on the 2.5-m system. We present new transformation equations and discuss applications of these data to future low-mass star studies using the SDSS., Comment: 8 Pages, 5 Figures. Accepted to AJ

We present the selection algorithm and anticipated results for the Time Domain Spectroscopic Survey (TDSS). TDSS is an Sloan Digital Sky Survey (SDSS)-IV Extended Baryon Oscillation Spectroscopic Survey (eBOSS) subproject that will provide initial identification spectra of approximately 220,000 luminosity-variable objects (variable stars and active galactic nuclei across 7500 deg2 selected from a combination of SDSS and multi-epoch Pan-STARRS1 photometry. TDSS will be the largest spectroscopic survey to explicitly target variable objects, avoiding pre-selection on the basis of colors or detailed modeling of specific variability characteristics. Kernel Density Estimate analysis of our target population performed on SDSS Stripe 82 data suggests our target sample will be 95% pure (meaning 95% of objects we select have genuine luminosity variability of a few magnitudes or more). Our final spectroscopic sample will contain roughly 135,000 quasars and 85,000 stellar variables, approximately 4000 of which will be RR Lyrae stars which may be used as outer Milky Way probes. The variability-selected quasar population has a smoother redshift distribution than a color-selected sample, and variability measurements similar to those we develop here may be used to make more uniform quasar samples in large surveys. The stellar variable targets are distributed fairly uniformly across color space, indicating that TDSS will obtain spectra for a wide variety of stellar variables including pulsating variables, stars with significant chromospheric activity, cataclysmic variables, and eclipsing binaries. TDSS will serve as a pathfinder mission to identify and characterize the multitude of variable objects that will be detected photometrically in even larger variability surveys such as Large Synoptic Survey Telescope.

We present an analysis of the starspots on the active M4 dwarf GJ 1243, using 4 years of time series photometry from Kepler. A rapid P = 0.592596 ? 0.00021 days rotation period is measured due to the ?2.2% starspot-induced flux modulations in the light curve. We first use a light curve modeling approach, using a Monte Carlo Markov Chain sampler to solve for the longitudes and radii of the two spots within 5 day windows of data. Within each window of time the starspots are assumed to be unchanging. Only a weak constraint on the starspot latitudes can be implied from our modeling. The primary spot is found to be very stable over many years. A secondary spot feature is present in three portions of the light curve, decays on 100?500 day timescales, and moves in longitude over time. We interpret this longitude shearing as the signature of differential rotation. Using our models we measure an average shear between the starspots of 0.0047 rad day?1, which corresponds to a differential rotation rate of ? = 0.012 ? 0.002 rad day?1. We also fit this starspot phase evolution using a series of bivariate Gaussian functions, which provides a consistent shear measurement. This is among the slowest differential rotation shear measurements yet measured for a star in this temperature regime, and provides an important constraint for dynamo models of low-mass stars.

We present multi-color transformations and photometric parallaxes for a sample of 40 low mass dwarfs selected from the Sloan Digital Sky Survey (SDSS) and the General Catalog of Trigonometric Stellar Parallaxes. Our sample was re-observed at the Manastash Ridge Observatory (MRO) using both Sloan and Johnson-Cousin filters and color transformations between the two photometric systems were derived. A subset of the sample had previously measured Johnson-Cousins photometry and parallaxes as well as 2MASS photometry. We observed these stars at MRO using Sloan filters and used these data to derive photometric parallax relations as well as SDSS/Johnson-Cousins/2MASS color transformations. We present the data and derived transformations for use in future low mass star studies., Comment: 7 pages, Accepted for publication in PASP

We analyzed Kepler short-cadence M dwarf observations. Spectra from the ARC 3.5m telescope identify magnetically active (H$\alpha$ in emission) stars. The active stars are of mid-M spectral type, have numerous flares, and well-defined rotational modulation due to starspots. The inactive stars are of early-M type, exhibit less starspot signature, and have fewer flares. A Kepler to U-band energy scaling allows comparison of the Kepler flare frequency distributions with previous ground-based data. M dwarfs span a large range of flare frequency and energy, blurring the distinction between active and inactive stars designated solely by the presence of H$\alpha$. We analyzed classical and complex (multiple peak) flares on GJ 1243, finding strong correlations between flare energy, amplitude, duration and decay time, with only a weak dependence on rise time. Complex flares last longer and have higher energy at the same amplitude, and higher energy flares are more likely to be complex. A power law fits the energy distribution for flares with log $E_{K_p} >$ 31 ergs, but the predicted number of low energy flares far exceeds the number observed, at energies where flares are still easily detectable, indicating that the power law distribution may flatten at low energy. There is no correlation of flare occurrence or energy with starspot phase; the flare waiting time distribution is consistent with flares occurring randomly in time; and the energies of consecutive flares are uncorrelated. These observations support a scenario where many independent active regions on the stellar surface are contributing to the observed flare rate., Comment: 16 pages, 14 figures, ApJ Accepted

We present the largest sample of flares ever compiled for a single M dwarf, the active M4 star GJ 1243. Over 6100 individual flare events, with energies ranging from $10^{29}$ to $10^{33}$ erg, are found in 11 months of 1-minute cadence data from Kepler. This sample is unique for its completeness and dynamic range. We have developed automated tools for finding flares in short-cadence Kepler light curves, and performed extensive validation and classification of the sample by eye. From this pristine sample of flares we generate a median flare template. This template shows that two exponential cooling phases are present during the white-light flare decay, providing fundamental constraints for models of flare physics. The template is also used as a basis function to decompose complex multi-peaked flares, allowing us to study the energy distribution of these events. Only a small number of flare events are not well fit by our template. We find that complex, multi-peaked flares occur in over 80% of flares with a duration of 50 minutes or greater. The underlying distribution of flare durations for events 10 minutes and longer appears to follow a broken power law. Our results support the idea that sympathetic flaring may be responsible for some complex flare events., 12 pages, 9 figures, accepted for publication in ApJ

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) - one of the Sloan Digital Sky Survey III programs -- is using near-infrared spectra of $\sim 100,000$ red giant branch star candidates to study the structure of the Milky Way. In the course of the survey, APOGEE also acquires spectra of hot field stars to serve as telluric calibrators for the primary science targets. We report the serendipitous discovery of two rare, fast-rotating B stars of the $\sigma$ Ori E type among those blue field stars observed during the first year of APOGEE operations. Both of the discovered stars display the spectroscopic signatures of the rigidly rotating magnetospheres (RRM) common to this class of highly-magnetized ($B \sim 10$ kiloGauss) stars, increasing the number of known RRM stars by $\sim 10 \%$. One (HD 345439) is a main-sequence B star with unusually strong He absorption (similar to $\sigma$ Ori E), while the other (HD 23478) fits a "He-normal" B3IV classification. We combine the APOGEE discovery spectra with other optical and near-infrared spectra of these two stars, and of $\sigma$ Ori E itself, to show how near-infrared spectroscopy can be a uniquely powerful tool for discovering more of these rare objects, which may show little/no RRM signatures in their optical spectra. We discuss the potential for further discovery of $\sigma$ Ori E type stars, as well as the implications of our discoveries for the population of these objects and insights into their origin and evolution., Comment: 14 pages, incl. 5 figures; accepted for publication in ApJ Letters

We present and discuss an extensive data set for the non-Blazhko ab-type RR Lyrae star SDSSJ015450+001501, including optical SDSS ugriz light curves and spectroscopic data, LINEAR and CSS unfiltered optical light curves, and infrared 2MASS JHKs and WISE W1 and W2 light curves. Most notably, light curves obtained by 2MASS include close to 9000 photometric measures collected over 3.3 years and provide exceedingly precise view of near-IR variability. These data demonstrate that static atmosphere models are insufficient to explain multi-band photometric light curve behavior and present strong constraints for non-linear pulsation models for RR Lyrae stars. It is a challenge to modelers to produce theoretical light curves that can explain data presented here, which we make publicly available., Comment: 8 pages, 8 figures. Accepted for publication in ApJ. Online tables are available upon request, or can be downloaded the first author's website

We present a homogeneous survey of line and continuum emission from near-ultraviolet (NUV) to optical wavelengths during twenty M dwarf flares with simultaneous, high cadence photometry and spectra. These data were obtained to study the white-light continuum components at bluer and redder wavelengths than the Balmer jump. Our goals were to break the degeneracy between emission mechanisms that have been fit to broadband colors of flares and to provide constraints for radiative-hydrodynamic (RHD) flare models that seek to reproduce the white-light flare emission. The main results from the continuum analysis are the following: 1) the detection of Balmer continuum (in emission) that is present during all flares and with a wide range of relative contributions to the continuum flux at bluer wavelengths than the Balmer jump; 2) a blue continuum at flare maximum that is linearly decreasing with wavelength from \lambda = 4000-4800\AA, matched by the spectral shape of hot, blackbody emission with typical temperatures of T_{BB}~9000-14,000 K; 3) a redder continuum apparent at wavelengths longer than H\beta\ (\lambda > 4900\AA) which becomes relatively more important to the energy budget during the late gradual phase. We calculate Balmer jump flux ratios and compare to RHD model spectra. The model ratios are too large and the blue-optical (\lambda = 4000-4800\AA) slopes are too red in both the impulsive and gradual decay phases of all twenty flares. This discrepancy implies that further work is needed to understand the heating at high column mass during dMe flares. (Abridged), Comment: published in the Astrophysical Journal Supplement Series; data available through VizieR in July. arXiv version notes: 203 pages, 66 figures, 1 online-only figure set, 11 tables, Appendix C Figure 62 excluded (see published article)

By selecting astrometric and photometric data from the Sloan Digital Sky Survey (SDSS), the L{��}pine & Shara Proper Motion North Catalog (LSPM-North), the Two Micron All Sky Survey (2MASS), and the USNO-B1.0 catalog, we use a succession of methods to isolate white dwarf candidates for follow-up spectroscopy. Our methods include: reduced proper motion diagram cuts, color cuts, and atmospheric model adherence. We present spectroscopy of 26 white dwarfs obtained from the CTIO 4m and APO 3.5m telescopes. Additionally, we confirm 28 white dwarfs with spectra available in the SDSS DR7 database but unpublished elsewhere, presenting a total of 54 WDs. We label one of these as a recovered WD while the remaining 53 are new discoveries. We determine physical parameters and estimate distances based on atmospheric model analyses. Three new white dwarfs are modeled to lie within 25 pc. Two additional white dwarfs are confirmed to be metal-polluted (DAZ). Follow-up time series photometry confirms another object to be a pulsating ZZ Ceti white dwarf., 9 figures, 3 Tables; http://stacks.iop.org/1538-3881/143/103

We present a spectroscopic catalog of 70,841 visually inspected M dwarfs from the seventh data release of the Sloan Digital Sky Survey (SDSS). For each spectrum, we provide measurements of the spectral type, a number of molecular bandheads, and the H-alpha, H-beta, H-gamma, H-delta and Ca II K emission lines. In addition, we calculate the metallicity-sensitive parameter zeta and identify a relationship between zeta and the g-r and r-z colors of M dwarfs. We assess the precision of our spectral types (which were assigned by individual examination), review the bulk attributes of the sample, and examine the magnetic activity properties of M dwarfs, in particular those traced by the higher order Balmer transitions. Our catalog is cross-matched to Two Micron All Sky Survey (2MASS) infrared data, and contains photometric distances for each star. Lastly, we identify eight new late-type M dwarfs that are possibly within 25 pc of the Sun. Future studies will use these data to thoroughly examine magnetic activity and kinematics in late-type M dwarfs and examine the chemical and dynamical history of the local Milky Way., Comment: 14 pages, 10 figures, 5 tables (in emulateapj format), accepted for publication in the Astronomical Journal