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Thermal bombs are a widely used method to artificially trigger explosions of core-collapse supernovae (CCSNe) to determine their nucleosynthesis or ejecta and remnant properties. Recently, their use in spherically symmetric (1D) hydrodynamic simulations led to the result that {56,57}Ni and 44Ti are massively underproduced compared to observational estimates for Supernova 1987A, if the explosions are slow, i.e., if the explosion mechanism of CCSNe releases the explosion energy on long timescales. It was concluded that rapid explosions are required to match observed abundances, i.e., the explosion mechanism must provide the CCSN energy nearly instantaneously on timescales of some ten to order 100 ms. This result, if valid, would disfavor the neutrino-heating mechanism, which releases the CCSN energy on timescales of seconds. Here, we demonstrate by 1D hydrodynamic simulations and nucleosynthetic post-processing that these conclusions are a consequence of disregarding the initial collapse of the stellar core in the thermal-bomb modelling before the bomb releases the explosion energy. We demonstrate that the anti-correlation of 56Ni yield and energy-injection timescale vanishes when the initial collapse is included and that it can even be reversed, i.e., more 56Ni is made by slower explosions, when the collapse proceeds to small radii similar to those where neutrino heating takes place in CCSNe. We also show that the 56Ni production in thermal-bomb explosions is sensitive to the chosen mass cut and that a fixed mass layer or fixed volume for the energy deposition cause only secondary differences. Moreover, we propose a most appropriate setup for thermal bombs., 24 pages, 12 figures; version accepted by MNRAS after minor revision

Abdurro’uf et al., This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 survey that publicly releases infrared spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the subsurvey Time Domain Spectroscopic Survey data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey subsurvey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated value-added catalogs. This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper, Local Volume Mapper, and Black Hole Mapper surveys., This publication uses data generated via the Zooniverse.org platform, development of which is funded by generous support, including a Global Impact Award from Google, and by a grant from the Alfred P. Sloan Foundation. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.

The mass of a star is the most fundamental parameter for its structure, evolution, and final fate. It is particularly important for any kind of stellar archaeology and characterization of exoplanets. There exist a variety of methods in astronomy to estimate or determine it. In this review we present a significant number of such methods, beginning with the most direct and model-independent approach using detached eclipsing binaries. We then move to more indirect and model-dependent methods, such as the quite commonly used isochrone or stellar track fitting. The arrival of quantitative asteroseismology has opened a completely new approach to determine stellar masses and to complement and improve the accuracy of other methods. We include methods for different evolutionary stages, from the pre-main sequence to evolved (super)giants and final remnants. For all methods uncertainties and restrictions will be discussed. We provide lists of altogether more than 200 benchmark stars with relative mass accuracies between [0.3 , 2] % for the covered mass range of M∈[0.1,16]M⊙, 75 % of which are stars burning hydrogen in their core and the other 25 % covering all other evolved stages. We close with a recommendation how to combine various methods to arrive at a “mass-ladder” for stars., The authors are much indebted to all colleagues participating in the workshop, even though they were not involved in the textual contributions for this review paper. A.S. acknowledges support from Grants ESP2017-82674-R and PID2019-108709GB-I00 (MICINN) and 2017-SGR-1131 (AGAUR). C.A., J.S.G.M., and M.G.P. received funding from the European Research Council (ERC) under the European Union?s Horizon 2020 research and innovation programme (Grant agreement no.?670519: MAMSIE) and from the KU?Leuven Research Council (grant C16/18/005: PARADISE). M.B. is supported through the Lise Meitner grant from the Max Planck Society and acknowledges support by the Collaborative Research centre SFB 881 (projects A5, A10), Heidelberg University, of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). V.S.A. acknowledges support from the Independent Research Fund Denmark (Research grant 7027-00096B) and the Carlsberg foundation (Grant agreement CF19-0649). Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant agreement No.?DNRF106). D.B., J.C.M., and I.R. acknowledge support from the Spanish Ministry of Science, Innovation and Universities (MICIU), and the Fondo Europeo de Desarrollo Regional (FEDER) through Grants ESP2016-80435-C2-1-R and PGC2018-098153-B-C33, as well as the support of the Generalitat de Catalunya (CERCA programme). N.B. gratefully acknowledge financial support from the Royal Society (University Research Fellowships) and from the European Research Council (ERC-CoG-646928, Multi-Pop). A.E. acknowledges support from the Research Foundation Flanders (FWO) under contract ZKD1501-00-W01 (Grant no. 792848). D.K.F. acknowledges funds from the Alexander von Humboldt Foundation in the framework of the Sofia Kovalevskaja Award endowed by the Federal Ministry of Education and Research and grant 2016-03412 from the Swedish Research Council. D.G. gratefully acknowledges financial support from the CRT foundation under Grant no. 2018.2323 ?Gaseous or rocky? Unveiling the nature of small worlds ?. L.G. acknowledges funding from LSST-Italy and from project MITiC 2015. N.L. was financially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under Grant number AYA2015-69350-C3-2-P. A.M. acknowledges funding from the European Union?s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No?749962 (project THOT). B.N. is supported by Funda??o para a Ci?ncia e a Tecnologia (FCT, Portugal) under Grant PD/BD/113744/2015 from PhD::SPACE, an FCT PhD program, and by the Alexander von?Humboldt Foundation. Further support from FEDER ? Fundo Europeu de Desenvolvimento Regional funds through the COMPETE 2020 ? Operacional Programme for Competitiveness and Internationalisation (POCI), and by Portuguese funds through FCT ? Funda??o para a Ci?ncia e a Tecnologia in the framework of the Project POCI-01-0145-FEDER-030389 is also acknowledged. K.P. acknowledges support from the Croatian Science Foundation (HRZZ research Grant IP-2014-09-8656). P-E.T. has received funding from the European Research Council under the European Union?s Horizon 2020 research and innovation programme n.?677706 (WD3D). The authors thank our colleagues G.?Bono, T.L.?Campante, M.S.?Cunha, P. Das, C.?Johnston, F.?Kiefer, P.?Maxted, M.J.P.F.G.?Monteiro, Th.?Rodrigues, V. Schaffenroth, M. Vu?kovi? for helpful comments and useful discussions. This work presents results from the European Space Agency (ESA) space mission Gaia and from the American National Aeronautics and Space Administration (NASA) space missions Kepler and TESS.

We calculate models of stellar evolution for very massive stars and include the effects of modified gravity to investigate the influence on the physical properties of blue supergiant stars and their use as extragalactic distance indicators. With shielding and fifth force parameters in a similar range as in previous studies of Cepheid and tip of the red giant branch (TRGB) stars we find clear effects on stellar luminosity and flux-weighted gravity. The relationship between flux weighted gravity, g_F = g/Teff^4, and bolometric magnitude M_bol (FGLR), which has been used successfully for accurate distance determinations, is systematically affected. While the stellar evolution FGLRs show a systematic offset from the observed relation, we can use the differential shifts between models with Newtonian and modified gravity to estimate the influence on FGLR distance determinations. Modified gravity leads to a distance increase of 0.05 to 0.15 magnitudes in distance modulus. These change are comparable to the ones found for Cepheid stars. We compare observed FGLR and TRGB distances of nine galaxies to constrain the free parameters of modified gravity. Not accounting for systematic differences between TRGB and FGLR distances shielding parameters of 5*10^-7 and 10^-6 and fifth force parameters of 1/3 and 1 can be ruled out with about 90% confidence. Allowing for potential systematic offsets between TRGB and FGLR distances no determination is possible for a shielding parameter of 10^-6. For 5*10$^-7 a fifth force parameter of 1 can be ruled out to 92% but 1/3 is unlikely only to 60%., To be published in the Astrophysical Journal

1D stellar evolution codes employ rudimentary treatments of turbulent convection. For stars with convective envelopes, this leads to systematic errors in the predicted oscillation frequencies needed for asteroseismology. One way of mending these structural inadequacies is through patching, whereby the outermost layers of 1D models are replaced by the mean stratifications from 3D simulations. In order to viably implement this approach in asteroseismic analysis, interpolation throughout precomputed 3D envelopes is required. We present a method that interpolates throughout precomputed 3D envelopes as a function of effective temperature, surface gravity, and metallicity. We conduct a series of validation tests that demonstrate that the scheme reliably and accurately reproduces the structures of stellar envelopes and apply our method to the Sun as well as two stars observed by Kepler. We parameterize the frequency shift that results from patching and show that the functional forms are evolutionary dependent. In addition we find that neglecting modal effects, such as non-adiabatic energetics, introduces systematic errors in asteroseimically obtained stellar parameters. Both these results suggest that a cautious approach is necessary when utilizing empirical surface corrections in lieu of patching models. Our results have important implications, particularly for characterizing exoplanet systems, where accuracy is of utmost concern., Comment: 17 pages, 14 figures

In a series of papers, we have recently demonstrated that it is possible to construct stellar structure models that robustly mimic the stratification of multi-dimensional radiative magneto-hydrodynamic simulations at every time-step of the computed evolution. The resulting models offer a more realistic depiction of the near-surface layers of stars with convective envelopes than parameterizations, such as mixing length theory, do. In this paper, we explore how this model improvement impacts on seismic and non-seismic properties of stellar models across the Hertzsprung-Russell diagram. We show that the improved description of the outer boundary layers alters the predicted global stellar properties at different evolutionary stages. In a hare and hound exercise, we show that this plays a key role for asteroseismic analyses, as it, for instance, often shifts the inferred stellar age estimates by more than 10 per cent. Improper boundary conditions may thus introduce systematic errors that exceed the required accuracy of the PLATO space mission. Moreover, we discuss different approximations for how to compute stellar oscillation frequencies. We demonstrate that the so-called gas $\Gamma_1$ approximation performs reasonably well for all main-sequence stars. Using a Monte Carlo approach, we show that the model frequencies of our hybrid solar models are consistent with observations within the uncertainties of the global solar parameters when using the so-called reduced $\Gamma_1$ approximation., Comment: Submitted to MNRAS

Convective boundary mixing (CBM) is ubiquitous in stellar evolution. It is a necessary ingredient in the models in order to match observational constraints from clusters, binaries and single stars alike. We compute `effective overshoot' measures that reflect the extent of mixing and which can differ significantly from the input overshoot values set in the stellar evolution codes. We use constraints from pressure modes to infer the CBM properties of Kepler and CoRoT main-sequence and subgiant oscillators, as well as in two radial velocity targets (Procyon A and $\alpha$ Cen A). Collectively these targets allow us to identify how measurement precision, stellar spectral type, and overshoot implementation impact the asteroseismic solution. With these new measures we find that the `effective overshoot' for most stars is in line with physical expectations and calibrations from binaries and clusters. However, two F-stars in the CoRoT field (HD 49933 and HD 181906) still necessitate high overshoot in the models. Due to short mode lifetimes, mode identification can be difficult in these stars. We demonstrate that an incongruence between the radial and non-radial modes drives the asteroseismic solution to extreme structures with highly-efficient CBM as an inevitable outcome. Understanding the cause of seemingly anomalous physics for such stars is vital for inferring accurate stellar parameters from TESS data with comparable timeseries length., Comment: 20 Pages, 9 Figures, 4 Tables and supplementary material. Accepted for publication in MNRAS

The treatment of convective boundaries remains an important source of uncertainty within stellar evolution, with drastic implications for the thermally-pulsing stars on the Asymptotic Giant Branch (AGB). Various sources are taken as motivation for the incorporation of convective boundary mixing during this phase, from s-process nucleosynthesis to hydrodynamical models. In spite of the considerable evidence in favour of the existence of convective boundary mixing on the pre-AGB evolution, this mixing is not universally included in models of TP-AGB stars. The aim of this investigation is to ascertain the extent of convective boundary mixing, which is compatible with observations when considering full evolutionary models. Additionally, we investigate a theoretical argument that has been made that momentum-driven overshooting at the base of the pulse-driven convection zone should be negligible. We show that, while the argument holds,estimations based on the picture of turbulent entrainment suggest that mixing is possible at both convective boundaries. We demonstrate that additional mixing at convective boundaries during core-burning phases prior to the thermally-pulsing Asymptotic Giant Branch has an impact on the later evolution, changing the mass range at which the third dredge-up and hot-bottom burning occur, and thus also the final surface composition. In addition, an effort has been made to constrain the efficiency of convective boundary mixing at the different convective boundaries, using observational constraints. Our study suggests a strong tension between different constraints that makes it impossible to reproduce all observables simultaneously within the framework of an exponentially decaying overshooting. This result calls for a reassessment of both the models of convective boundary mixing and the observational constraints., Instituto de Astrofísica de La Plata

The South Pole Telescope (SPT) has systematically identified 81 high-redshift, strongly gravitationally lensed, dusty star-forming galaxies (DSFGs) in a 2500 square degree cosmological mm-wave survey. We present the final spectroscopic redshift survey of this flux-limited ($S_{870\, \mathrm{\mu m}} > 25\, \mathrm{mJy}$) sample, initially selected at $1.4$ mm. The redshift survey was conducted with the Atacama Large Millimeter/submillimeter Array across the $3$ mm spectral window, targeting carbon monoxide line emission. By combining these measurements with ancillary data, the SPT sample is now spectroscopically complete, with redshifts spanning $1.9$$$$5$, making this the largest sample of high-redshift DSFGs to-date, and enabling the "high-redshift tail" of extremely luminous DSFGs to be measured. Though galaxy formation models struggle to account for the SPT redshift distribution, the larger sample statistics from this complete and well-defined survey will help inform future theoretical efforts., Comment: 56 pages, 25 figures, accepted for publication in ApJ

Standard 1D stellar evolution models do not correctly reproduce the structure of the outermost layers of stars with convective envelopes. This has been a long-standing problem in stellar modelling affecting both the predicted evolutionary paths and the attributed oscillation frequencies, and indirectly biasing numerous quantities derived from stellar evolution calculations. We present a novel method that mostly eliminates these structural defects by appending mean 3D simulations of stellar envelopes. In contrast to previous attempts we impose the complete structure derived from 3D simulations at each time step during the entire evolution. For this purpose, we interpolate in grids of pre-computed 3D simulations and use the resulting structure as boundary conditions, in order to solve the stellar structure equations for the 1D interior at each time step. Our method provides a continuous transition in many quantities from the interior to the imposed interpolated 3D surface layers. We present a solar calibration model and show that the obtained structure of the surface layers reliably mimics that of the underlying 3D simulations for the present Sun. Moreover, we perform a helioseismic analysis, showing that our method mostly eliminates the structural contribution to the discrepancy between model frequencies and observed p-mode frequencies., 5 pages, 5, figures, MNRAS Letter

Models of stellar structure and evolution are an indispensable tool in astrophysics, yet they are known to incorrectly reproduce the outer convective layers of stars. In the first paper of this series, we presented a novel procedure to include the mean structure of 3D hydrodynamical simulations on-the-fly in stellar models, and found it to significantly improve the outer stratification and oscillation frequencies of a standard solar model. In the present work, we extend the analysis of the method; specifically how the transition point between envelope and interior affects the models. We confirm the versatility of our method by successfully repeating the entire procedure for a different grid of 3D hydro-simulations. Furthermore, the applicability of the procedure was investigated across the HR diagram and an accuracy comparable to the solar case was found. Moreover, we explored the implications on stellar evolution and find that the red-giant branch is shifted about 40 K to higher effective temperatures. Finally, we present for the first time an asteroseismic analysis based on stellar models fully utilising the stratification of 3D simulations on-the-fly. These new models significantly reduce the asteroseismic surface term for the two selected stars in the Kepler field. We extend the analysis to red giants and characterise the shape of the surface effect in this regime. Lastly, we stress that the interpolation required by our method would benefit from new 3D simulations, resulting in a finer sampling of the grid., 14 pages, 13 figures, 4 tables. Accepted for publication in MNRAS

Context The Vela Molecular Ridge is one of the nearest (700 pc) giant molecular cloud (GMC) complexes hosting intermediate-mass (up to early B, late O stars) star formation, and is located in the outer Galaxy, inside the Galactic plane. Vela C is one of the GMCs making up the Vela Molecular Ridge, and exhibits both sub-regions of robust and sub-regions of more quiescent star formation activity, with both low- and intermediate(high)-mass star formation in progress. Aims We aim to study the individual and global properties of dense dust cores in Vela C, and aim to search for spatial variations in these properties which could be related to different environmental properties and/or evolutionary stages in the various sub-regions of Vela C. Methods We mapped the submillimetre (345 GHz) emission from vela C with LABOCA (beam size 19.2", spatial resolution ~0.07 pc at 700 pc) at the APEX telescope. We used the clump-finding algorithm CuTEx to identify the compact submillimetre sources. We also used SIMBA (250 GHz) observations, and Herschel and WISE ancillary data. The association with WISE red sources allowed the protostellar and starless cores to be separated, whereas the Herschel dataset allowed the dust temperature to be derived for a fraction of cores. The protostellar and starless core mass functions (CMFs) were constructed following two different approaches, achieving a mass completeness limit of 3.7 Msun. Results We retrieved 549 submillimetre cores, 316 of which are starless and mostly gravitationally bound (therefore prestellar in nature). Both the protostellar and the starless CMFs are consistent with the shape of a Salpeter initial mass function in the high-mass part of the distribution. Clustering of cores at scales of 1--6 pc is also found, hinting at fractionation of magnetised, turbulent gas., Comment: 21 pages, 19 figures, to be published in Astronomy & Astrophysics

State-of-the-art one-dimensional (1D) stellar evolution codes rely on simplifying assumptions, such as mixing length theory, in order to describe superadiabatic convection. As a result, 1D stellar structure models do not correctly recover the surface layers of the Sun and other stars with convective envelopes. We present a method that overcomes this structural drawback by employing three-dimensional (3D) hydrodynamic simulations of stellar envelopes: at every time-step of the evolution interpolated 3D envelopes are appended to the 1D structure and are used to supply realistic boundary conditions for the stellar interior. In contrast to previous attempts, our method includes mean 3D turbulent pressure. We apply our method to model the present Sun. The structural shortcomings of standard stellar models lead to systematic errors in the stellar oscillation frequencies inferred from the model. We show that our method fully corrects for this error. Furthermore, we show that our realistic treatment of superadiabatic convection alters the predicted evolution of the Sun. Our results hence have important implications for the characterization of stars. This has ramifications for neighbouring fields, such as exoplanet research and galactic archaeology, for which accurate stellar models play a key role., 11 pages, 8 figures, 1 table, accepted for publication in MNRAS

Recent observational programmes are providing a global view of the Milky Way bulge that serves as template for detailed comparison with models and extragalactic bulges. A number of surveys (i.e. VVV, GIBS, GES, ARGOS, BRAVA, APOGEE) are producing comprehensive and detailed extinction, metallicity, kinematics and stellar density maps of the Galactic bulge with unprecedented accuracy. However, the still missing key ingredient is the distribution of stellar ages across the bulge. To overcome this limitation, we aim to age-date the stellar population in several bulge fields with the ultimate goal of deriving an age map of the Bulge. This paper presents the methodology and the first results obtained for a field along the Bulge minor axis, at $b=-6^\circ$. We use a new PSF-fitting photometry of the VISTA Variables in the V\'{i}a L\'{a}ctea (VVV) survey data to construct deep color-magnitude diagrams of the bulge stellar population down to $\sim$ 2 mag below the Main Sequence turnoff. We find the bulk of the bulge stellar population in the observed field along the minor axis to be at least older than $\sim$ 7.5 Gyr. In particular, when the metallicity distribution function spectroscopically derived by GIBS is used, the best fit to the data is obtained with a combination of synthetic populations with ages in between $\sim$ 7.5 Gyr and 11 Gyr. However, the fraction of stars younger than $\sim$ 10 Gyr strongly depends upon the number of Blue Straggler Stars present in the bulge. Simulations show that the observed color-magnitude diagram of the bulge in the field along the minor axis is incompatible with the presence of a conspicuous population of intermediate-age/young (i.e. $\lesssim 5$ Gyr) stars., Comment: 14 pages, 7 figues, Accepted for publication on A&A

We combine high-resolution ALMA and HST/CANDELS observations of 20 submillimeter galaxies (SMGs) predominantly from the AS2UDS survey at z~2 with bright rest-frame optical counterparts (Ks < 22.9) to investigate the resolved structural properties of their dust and stellar components. We derive two-dimensional stellar-mass distributions that are inferred from spatial mass-to-light ratio (M/L) corrections based on rest-frame optical colors. Due to the high central column densities of dust in our SMGs, our mass distributions likely represent a lower limit to the true central mass density. The centroid positions between the inferred stellar-mass and the dust distributions agree within 1.1 kpc, indicating an overall good spatial agreement between the two components. The majority of our sources exhibit compact dust configurations relative to the stellar component (with a median ratio of effective radii Re,dust/Re,Mstar = 0.6). This ratio does not change with specific star-formation rate (sSFR) over the factor of 30 spanned by our targets, sampling the locus of "normal" main sequence galaxies up to the starburst regime, log(sSFR/sSFRMS) > 0.5. Our results imply that massive SMGs are experiencing centrally enhanced star formation unlike typical spiral galaxies in the local Universe. The sizes and stellar densities of our SMGs are in agreement with those of the passive population at z=1.5, consistent with these systems being the descendants of z~2 SMGs., 26 pages, 11 figures, accepted for publication in ApJ

Current standard solar models neither account properly for the photospheric lithium abundance nor reproduce the inferred solar sound speed profile. Diffusive overshooting at the base of the solar convective envelope has previously been shown to solve either of these model inadequacies. In this paper, we present an analysis of solar models with four different parametrizations of diffusive overshooting. We find that these models are able to recover the correct lithium depletion, regardless of the parametrization, if overshooting is suppressed, during the early evolutionary stages. Further, parametrizations of diffusive overshooting have been shown to improve the inferred sound speed profile. However, none of the presented models are able to simultaneously solve both model inadequacies, showing that diffusive overshooting on its own is deficient to account for observations., 8 pages, 6 figures

Stellar evolution codes play a major role in present-day astrophysics, yet they share common simplifications related to the outer layers of stars. We seek to improve on this by the use of results from realistic and highly detailed 3D hydrodynamics simulations of stellar convection. We implement a temperature stratification extracted directly from the 3D simulations into two stellar evolution codes to replace the simplified atmosphere normally used. Our implementation also contains a non-constant mixing-length parameter, which varies as a function of the stellar surface gravity and temperature -- also derived from the 3D simulations. We give a detailed account of our fully consistent implementation and compare to earlier works, and also provide a freely available MESA-module. The evolution of low-mass stars with different masses is investigated, and we present for the first time an asteroseismic analysis of a standard solar model utilising calibrated convection and temperature stratification from 3D simulations. We show that the inclusion of 3D results have an almost insignificant impact on the evolution and structure of stellar models -- the largest effect are changes in effective temperature of order 30 K seen in the pre-main sequence and in the red-giant branch. However, this work provides the first step for producing self-consistent evolutionary calculations using fully incorporated 3D atmospheres from on-the-fly interpolation in grids of simulations., 10 pages, 9 figures. Accepted for publication in MNRAS

Stellar evolution codes play a major role in present-day astrophysics, yet they share common issues. In this work we seek to remedy some of those by the use of results from realistic and highly detailed 3D hydrodynamical simulations of stellar atmospheres. We have implemented a new temperature stratification extracted directly from the 3D simulations into the Garching Stellar Evolution Code to replace the simplified atmosphere normally used. Secondly, we have implemented the use of a variable mixing-length parameter, which changes as a function of the stellar surface gravity and temperature -- also derived from the 3D simulations. Furthermore, to make our models consistent, we have calculated new opacity tables to match the atmospheric simulations. Here, we present the modified code and initial results on stellar evolution using it., 4 pages, 5 figures; submitted to the conference proceedings: Seismology of the Sun and the Distant Stars 2016

Until recently, only a handful of dusty, star-forming galaxies (DSFGs) were known at $z>4$, most of them significantly amplified by gravitational lensing. Here, we have increased the number of such DSFGs substantially, selecting galaxies from the uniquely wide 250-, 350- and 500-$��$m Herschel-ATLAS imaging survey on the basis of their extremely red far-infrared colors and faint 350- and 500-$��$m flux densities - ergo they are expected to be largely unlensed, luminous, rare and very distant. The addition of ground-based continuum photometry at longer wavelengths from the JCMT and APEX allows us to identify the dust peak in their SEDs, better constraining their redshifts. We select the SED templates best able to determine photometric redshifts using a sample of 69 high-redshift, lensed DSFGs, then perform checks to assess the impact of the CMB on our technique, and to quantify the systematic uncertainty associated with our photometric redshifts, $��=0.14\,(1+z)$, using a sample of 25 galaxies with spectroscopic redshifts, each consistent with our color selection. For Herschel-selected ultrared galaxies with typical colors of $S_{500}/S_{250}\sim 2.2$ and $S_{500}/S_{350}\sim 1.3$ and flux densities, $S_{500}\sim 50\,$mJy, we determine a median redshift, $\hat{z}_{\rm phot}=3.66$, an interquartile redshift range, 3.30$-$4.27, with a median rest-frame 8$-$1000-$��$m luminosity, $\hat{L}_{\rm IR}$, of $1.3\times 10^{13}\,$L$_\odot$. A third lie at $z>4$, suggesting a space density, $��_{z>4}$, of $\approx 6 \times 10^{-7}\,$Mpc$^{-3}$. Our sample contains the most luminous known star-forming galaxies, and the most over-dense cluster of starbursting proto-ellipticals yet found., 22 pages; in press at The Astrophysical Journal; full-resolution PDF version available at http://www.roe.ac.uk/~rji/ivison2016.pdf

Solar p-mode oscillations exhibit a systematic offset towards higher frequencies due to shortcomings in the 1D stellar structure models, especially, the lack of turbulent pressure in the superadiabatic layers just below the optical surface, arising from the convective velocity field. We study the influence of the turbulent expansion, chemical composition, and magnetic fields on the stratification in the upper layers of the solar models in comparison with solar observations. Furthermore, we test alternative averages for improved results on the oscillation frequencies. We appended temporally and spatially averaged stratifications to 1D models to compute adiabatic oscillation frequencies that we then tested against observations. We also developed depth-dependent corrections for the solar 1D model, for which we expanded the geometrical depth to match the pressure stratification of the solar model, and we reduced the density that is caused by the turbulent pressure. We obtain the same results with our models as have been reported previously. Our depth-dependent corrected 1D models match the observations to almost a similar extent as the model. We find that correcting for the expansion of the geometrical depth and the reducing of the density are both equally necessary. Interestingly, the influence of the adiabatic exponent Gam1 is less pronounced than anticipated. The turbulent elevation directly from the model does not match the observations properly. Considering different reference depth scales for the averaging leads to very similar frequencies. Solar models with high metal abundances in their initial chemical composition match the low-frequency part much better. We find a linear relation between the p-mode frequency shift and the vertical magnetic field strength with dvnl = 26.21Bz microHz/kG, which is able to render the solar activity cycles correctly., 10 pages, 14 figures, accepted for publication in A&A

Recently Pasetto et al. have proposed a new method to derive a convection theory appropriate for the implementation in stellar evolution codes. Their approach is based on the simple physical picture of spherical bubbles moving within a potential flow in dynamically unstable regions, and a detailed computation of the bubble dynamics. Based on this approach, the authors derive a new theory of convection which is claimed to be parameter-free, non-local and time-dependent. This is a very strong claim, as such a theory is the holy grail of stellar physics. Unfortunately, we have identified several distinct problems in the derivation which ultimately render their theory inapplicable to any physical regime. In addition, we show that the framework of spherical bubbles in potential flows is unable to capture the essence of stellar convection, even when equations are derived correctly., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

Sensitive ground-based submillimeter surveys, such as ATLASGAL, provide a global view on the distribution of cold dense gas in the Galactic plane. Here we use the 353 GHz maps from the Planck/HFI instrument to complement the ground-based APEX/LABOCA observations with information on larger angular scales. The resulting maps reveal the distribution of cold dust in the inner Galaxy with a larger spatial dynamic range. We find examples of elongated structures extending over angular scales of 0.5 degree. Corresponding to >30 pc structures in projection at a distance of 3 kpc, these dust lanes are very extended and show large aspect ratios. Furthermore, we assess the fraction of dense gas ($f_{\rm DG}$), and estimate 2-5% (above A$_{\rm{v}}>$7 mag) on average in the Galactic plane. PDFs of the column density reveal the typically observed log-normal distribution for low- and exhibit an excess at high column densities. As a reference for extragalactic studies, we show the line-of-sight integrated N-PDF of the inner Galaxy, and derive a contribution of this excess to the total column density of $\sim2.2$%, above $N_{\rm H_2} = 2.92\times10^{22}$ cm$^{-2}$. Taking the total flux density, we provide an independent estimate of the mass of molecular gas in the inner Galaxy of $\sim1\times10^9\,M_{\odot}$, which is consistent with previous estimates using CO emission. From the mass and $f_{\rm DG}$ we estimate a Galactic SFR of $\dot M = 1.3\,M_{\odot}$ yr$^{-1}$. While the distribution of diffuse gas is homogenous in the inner Galaxy, the CMZ stands out with a higher dense gas fraction. The low star formation efficiency of the Milky Way is well explained by the low $f_{\rm DG}$ in the Galactic ISM, while the high $f_{\rm DG}$ towards the CMZ, despite its low star formation activity, suggests that, in that particular region of our Galaxy, high-density gas is not the bottleneck for star formation., Accepted for publication in A&A. 10 pages, 10 figures, abstract is shortened

Tracing molecular hydrogen content with carbon monoxide in low-metallicity galaxies has been exceedingly difficult. Here we present a new effort, with IRAM 30-m observations of 12CO(1-0) of a sample of 8 dwarf galaxies having oxygen abundances ranging from 12+logO/H=7.7 to 8.4. CO emission is detected in all galaxies, including the most metal-poor galaxy of our sample (0.1 Zsun); to our knowledge this is the largest number of 12CO(1-0) detections ever reported for galaxies with 12+logO/H, 18 pages, 15 figures, accepted for publication in A&A

We present spatially-resolved imaging obtained with the Australia Telescope Compact Array (ATCA) of three CO lines in two high-redshift gravitationally lensed dusty star-forming galaxies, discovered by the South Pole Telescope. Strong lensing allows us to probe the structure and dynamics of the molecular gas in these two objects, at z=2.78 and z=5.66, with effective source-plane resolution of less than 1kpc. We model the lensed emission from multiple CO transitions and the dust continuum in a consistent manner, finding that the cold molecular gas as traced by low-J CO always has a larger half-light radius than the 870um dust continuum emission. This size difference leads to up to 50% differences in the magnification factor for the cold gas compared to dust. In the z=2.78 galaxy, these CO observations confirm that the background source is undergoing a major merger, while the velocity field of the other source is more complex. We use the ATCA CO observations and comparable resolution Atacama Large Millimeter/submillimeter Array dust continuum imaging of the same objects to constrain the CO-H_2 conversion factor with three different procedures, finding good agreement between the methods and values consistent with those found for rapidly star-forming systems. We discuss these galaxies in the context of the star formation - gas mass surface density relation, noting that the change in emitting area with observed CO transition must be accounted for when comparing high-redshift galaxies to their lower redshift counterparts., 14 pages, 7 figures; accepted for publication in ApJ

We present the HERA CO-Line Extragalactic Survey (HERACLES), an atlas of CO emission from 18 nearby galaxies that are also part of The HI Nearby Galaxy Survey (THINGS) and the Spitzer Infrared Nearby Galaxies Survey (SINGS). We used the HERA multi-pixel receiver on the IRAM 30-m telescope to map the CO J=2-1 line over the full optical disk (defined by the isophotal radius r_25) of each target, at 13" angular resolution and 2.6 km/s velocity resolution. Here we describe the observations and reduction of the data and show channel maps, azimuthally averaged profiles, integrated intensity maps, and peak intensity maps. The implied H2 masses range from 7 \times 10^6 to 6 \times 10^9 M_sun, with four low metallicity dwarf irregular galaxies yielding only upper limits. In the cases where CO is detected, the integrated H2-to-HI ratios range from 0.02 - 1.13 and H2-to-stellar mass ratios from 0.01 to 0.25. Exponential scale lengths of the CO emission for our targets are in the range 0.8 - 3.2 kpc, or 0.2 \pm 0.05 r_25. The intensity-weighted mean velocity of CO matches that of HI very well, with a 1\sigma scatter of only 6 km/s. The CO J=2-1 / J=1-0 line ratio varies over a range similar to that found in the Milky Way and other nearby galaxies, \sim 0.6 - 1.0, with higher values found in the centers of galaxies. The typical line ratio, \sim 0.8, could be produced by optically thick gas with an excitation temperature of \sim 10 K., Comment: 28 pages, 34 figures, published in AJ (http://adsabs.harvard.edu/abs/2009AJ....137.4670L)

Using the most recent results about white dwarfs (WDs) in ten open clusters, we revisit semiempirical estimates of the initial-final mass relation (IFMR) in star clusters, with emphasis on the use of stellar evolution models. We discuss the influence of these models on each step of the derivation. One intention of our work is to use consistent sets of calculations both for the isochrones and the WD cooling tracks. The second one is to derive the range of systematic errors arising from stellar evolution theory. This is achieved by using different sources for the stellar models and by varying physical assumptions and input data. We find that systematic errors, including the determination of the cluster age, are dominating the initial mass values, while observational uncertainties influence the final mass primarily. After having determined the systematic errors, the initial-final mass relation allows us finally to draw conclusions about the physics of the stellar models, in particular about convective overshooting., Facultad de Ciencias Astronómicas y Geofísicas

We present Karl G. Jansky Very Large Array observations of the CO J=1-0 transition in a sample of four $z\sim2$ main sequence galaxies. These galaxies are in the blue sequence of star-forming galaxies at their redshift, and are part of the IRAM Plateau de Bure HIgh-$z$ Blue Sequence Survey (PHIBSS) which imaged them in CO J=3-2. Two galaxies are imaged here at high signal-to-noise, allowing determinations of their disk sizes, line profiles, molecular surface densities, and excitation. Using these and published measurements, we show that the CO and optical disks have similar sizes in main-sequence galaxies, and in the galaxy where we can compare CO J=1-0 and J=3-2 sizes we find these are also very similar. Assuming a Galactic CO-to-H$_2$ conversion, we measure surface densities of $\Sigma_{mol}\sim1200$ M$_\odot$pc$^{-2}$ in projection and estimate $\Sigma_{mol}\sim500-900$ M$_\odot$pc$^{-2}$ deprojected. Finally, our data yields velocity-integrated Rayleigh-Jeans brightness temperature line ratios $r_{31}$ that are approximately unity. In addition to the similar disk sizes, the very similar line profiles in J=1-0 and J=3-2 indicate that both transitions sample the same kinematics, implying that their emission is coextensive. We conclude that in these two main sequence galaxies there is no evidence for significant excitation gradients or a large molecular reservoir that is diffuse or cold and not involved in active star-formation. We suggest that $r_{31}$ in very actively star-forming galaxies is likely an indicator of how well mixed the star formation activity and the molecular reservoir are., Comment: To appear in ApJ

We report about a 230 GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). We installed VLBI equipment and measured the APEX station position to 1 cm accuracy (1 sigma). We then observed 3C 279 on 2012 May 7 in a 5 hour 230 GHz VLBI track with baseline lengths of 2800 M$\lambda$ to 7200 M$\lambda$ and a finest fringe spacing of 28.6 micro-arcseconds. Fringes were detected on all baselines with SNRs of 12 to 55 in 420 s. The correlated flux density on the longest baseline was ~0.3 Jy/beam, out of a total flux density of 19.8 Jy. Visibility data suggest an emission region, Comment: accepted for publication in A&A

Imaging polarimetry is an important tool for the study of cosmic magnetic fields. In our Galaxy, polarization levels of a few up to $\sim$10\% are measured in the submillimeter dust emission from molecular clouds and in the synchrotron emission from supernova remnants. Only few techniques exist to image the distribution of polarization angles, as a means of tracing the plane-of-sky projection of the magnetic field orientation. At submillimeter wavelengths, polarization is either measured as the differential total power of polarization-sensitive bolometer elements, or by modulating the polarization of the signal. Bolometer arrays such as LABOCA at the APEX telescope are used to observe the continuum emission from fields as large as $\sim0\fdg2$ in diameter. %Here we present the results from the commissioning of PolKa, a polarimeter for Here we present PolKa, a polarimeter for LABOCA with a reflection-type waveplate of at least 90\% efficiency. The modulation efficiency depends mainly on the sampling and on the angular velocity of the waveplate. For the data analysis the concept of generalized synchronous demodulation is introduced. The instrumental polarization towards a point source is at the level of $\sim0.1$\%, increasing to a few percent at the $-10$db contour of the main beam. A method to correct for its effect in observations of extended sources is presented. Our map of the polarized synchrotron emission from the Crab nebula is in agreement with structures observed at radio and optical wavelengths. The linear polarization measured in OMC1 agrees with results from previous studies, while the high sensitivity of LABOCA enables us to also map the polarized emission of the Orion Bar, a prototypical photon-dominated region.

We determine ages of 71 old Open Clusters by a two-step method: we use main-squence fitting to 10 selected clusters, in order to obtain their distances, and derive their ages from comparison with our own isochrones used before for Globular Clusters. We then calibrate the morphological age indicator delta(V), which can be obtained for all remaining clusters, in terms of age and metallicity. Particular care is taken to ensure consistency in the whole procedure. The resulting Open Cluster ages connect well to our previous Globular Cluster results. From the Open Cluster sample, as well as from the combined sample, questions regarding the formation process of Galactic components are addressed. The age of the oldest open clusters (NGC6791 and Be17) is of the order of 10 Gyr. We determine a delay by 2.0+-1.5 Gyr between the start of the halo and thin disk formation, whereas thin and thick disk started to form approximately at the same time. We do not find any significant age-metallicity relationship for the open cluster sample. The cumulative age distribution of the whole open cluster sample shows a moderately significant (~2sigma level) departure from the predictions for an exponentially declining dissolution rate with timescale of 2.5 Gyr. The cumulative age distribution does not show any trend with galactocentric distance, but the clusters with larger height to the Galactic plane have an excess of objects between 2-4 and 6 Gyr with respect to their counterpart closer to the plane of the Galaxy., Comment: Astronomy & Astrophysics, in press

Theoretical predictions of Red Giant Branch stars' effective temperatures, colors, luminosities and surface chemical abundances are a necessary tool for the astrophysical interpretation of the visible--near infrared integrated light from unresolved stellar populations, the Color-Magnitude-Diagrams of resolved stellar clusters and galaxies, and spectroscopic determinations of red giant chemical abundances. On the other hand, the comparison with empirical constraints provides a stringent test for the accuracy of present generations of red giant models. We review the current status of red giant stars' modelling, discussing in detail the still existing uncertainties affecting the model input physics (e.g., electron conduction opacity, treatment of the superadiabatic convection), and the adequacy of the physical assumptions built into the model computations. We compare theory with several observational features of the Red Giant Branch in galactic globular clusters, such as the luminosity function bump, the luminosity of the Red Giant Branch tip and the envelope chemical abundance patterns, to show the level of agreement between current stellar models and empirical data concerning the stellar luminosities, star counts, and surface chemical abundances., 71 pages, 18 figures, PASP review (in press)

We present direct constraints on the CO luminosity function at high redshift and the resulting cosmic evolution of the molecular gas density, $\rho_{\rm H2}$(z), based on a blind molecular line scan in the Hubble Deep Field North (HDF-N) using the IRAM Plateau de Bure Interferometer. Our line scan of the entire 3mm window (79-115 GHz) covers a cosmic volume of ~7000 Mpc$^3$, and redshift ranges z2. We use the rich multiwavelength and spectroscopic database of the HDF-N to derive some of the best constraints on CO luminosities in high redshift galaxies to date. We combine the blind CO detections in our molecular line scan (presented in a companion paper) with stacked CO limits from galaxies with available spectroscopic redshifts (slit or mask spectroscopy from Keck and grism spectroscopy from HST) to give first blind constraints on high-z CO luminosity functions and the cosmic evolution of the H2 mass density $\rho_{\rm H2}$(z) out to redshifts z~3. A comparison to empirical predictions of $\rho_{\rm H2}$(z) shows that the securely detected sources in our molecular line scan already provide significant contributions to the predicted $\rho_{\rm H2}$(z) in the redshift bins ~1.5 and ~2.7. Accounting for galaxies with CO luminosities that are not probed by our observations results in cosmic molecular gas densities $\rho_{\rm H2}$(z) that are higher than current predictions. We note however that the current uncertainties (in particular the luminosity limits, number of detections, as well as cosmic volume probed) are significant, a situation that is about to change with the emerging ALMA observatory., Comment: Accepted for publication in ApJ

We present a molecular line scan in the Hubble Deep Field North (HDF-N) that covers the entire 3mm window (79-115 GHz) using the IRAM Plateau de Bure Interferometer. Our CO redshift coverage spans z2. We reach a CO detection limit that is deep enough to detect essentially all z>1 CO lines reported in the literature so far. We have developed and applied different line searching algorithms, resulting in the discovery of 17 line candidates. We estimate that the rate of false positive line detections is ~2/17. We identify optical/NIR counterparts from the deep ancillary database of the HDF-N for seven of these candidates and investigate their available SEDs. Two secure CO detections in our scan are identified with star-forming galaxies at z=1.784 and at z=2.047. These galaxies have colors consistent with the `BzK' color selection and they show relatively bright CO emission compared with galaxies of similar dust continuum luminosity. We also detect two spectral lines in the submillimeter galaxy HDF850.1 at z=5.183. We consider an additional 9 line candidates as high quality. Our observations also provide a deep 3mm continuum map (1-sigma noise level = 8.6 $\mu$Jy/beam). Via a stacking approach, we find that optical/MIR bright galaxies contribute only to, Comment: Accepted for publication in ApJ

We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. The adiabatic entropy value of the deep convection zone, s_bot, and the entropy jump, {\Delta}s, determined from the 3D RHD models, are matched with the mixing length parameter, {\alpha}_MLT, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derive the mass mixing length, {\alpha}_m, and the vertical correlation length of the vertical velocity, C[v_z,v_z], directly from the 3D hydrodynamical simulations of stellar subsurface convection. The calibrated mixing length parameter for the Sun is {\alpha}_MLT (s_bot) = 1.98. For different stellar parameters, {\alpha}_MLT varies systematically in the range of 1.7 - 2.4. In particular, {\alpha}_MLT decreases towards higher effective temperature, lower surface gravity and higher metallicity. We find equivalent results for {\alpha}_MLT ({\Delta}s). Also, we find a tight correlation between the mixing length parameter and the inverse entropy jump. We derive an analytical expression from the hydrodynamic mean field equations that motivates the relation to the mass mixing length, {\alpha}_m, and find that it exhibits qualitatively a similar variation with stellar parameter (between 1.6 and 2.4) with a solar value of {\alpha}_m = 1.83. The vertical correlation length scaled with the pressure scale height yields for the Sun 1.71, but displays only a small systematic variation with stellar parameters, the correlation length slightly increasing with Teff. We derive mixing length parameters for various stellar parameters that can be used to replace a constant value. Within any convective envelope, {\alpha}_m and related quantities vary a lot., Comment: Accepted for publication in A&A, 15 pages, 20 figures, 2 tables

The red-giant branch (RGB) in globular clusters is extended to larger brightness if the degenerate helium core loses too much energy in "dark channels." Based on a large set of archival observations, we provide high-precision photometry for the Galactic globular cluster M5 (NGC 5904), allowing for a detailed comparison between the observed tip of the RGB with predictions based on contemporary stellar evolution theory. In particular, we derive 95% confidence limits of $g_{ae}, 5 pages, 2 figures, accepted for publication in Physical Review Letters

We present an Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 survey of 126 submillimeter sources from the LABOCA ECDFS Submillimeter Survey (LESS). Our 870 micron survey with ALMA (ALESS) has produced maps ~3X deeper and with a beam area ~200X smaller than the original LESS observations, doubling the current number of interferometrically-observed submillimeter sources. The high resolution of these maps allows us to resolve sources that were previously blended and accurately identify the origin of the submillimeter emission. We discuss the creation of the ALESS submillimeter galaxy (SMG) catalog, including the main sample of 99 SMGs and a supplementary sample of 32 SMGs. We find that at least 35% (possibly up to 50%) of the detected LABOCA sources have been resolved into multiple SMGs, and that the average number of SMGs per LESS source increases with LESS flux density. Using the (now precisely known) SMG positions, we empirically test the theoretical expectation for the uncertainty in the single-dish source positions. We also compare our catalog to the previously predicted radio/mid-infrared counterparts, finding that 45% of the ALESS SMGs were missed by this method. Our ~1.6" resolution allows us to measure a size of ~9 kpc X 5 kpc for the rest-frame ~300 um emission region in one resolved SMG, implying a star formation rate surface density of 80 M_sol yr^-1 kpc^-2, and we constrain the emission regions in the remaining SMGs to be, To appear in ApJ

Stellar evolution is modified if energy is lost in a "dark channel" similar to neutrino emission. Comparing modified stellar evolution sequences with observations provides some of the most restrictive limits on axions and other hypothetical low-mass particles and on non-standard neutrino properties. In particular, a putative neutrino magnetic dipole moment mu_nu enhances the plasmon decay process, postpones helium ignition in low-mass stars, and therefore extends the red-giant branch (RGB) in globular clusters (GCs). The brightness of the tip of the RGB (TRGB) remains the most sensitive probe for mu_nu and we revisit this argument from a modern perspective. Based on a large set of archival observations, we provide high-precision photometry for the Galactic GC M5 (NGC5904) and carefully determine its TRGB position. On the theoretical side, we add the extra plasmon decay rate brought about by mu_nu to the Princeton-Goddard-PUC stellar evolution code. Different sources of uncertainty are critically examined. The main source of systematic uncertainty is the bolometric correction and the main statistical uncertainty derives from the distance modulus based on main-sequence fitting. (Other measures of distance, e.g., the brightness of RR Lyrae stars, are influenced by the energy loss that we wish to constrain.) The statistical uncertainty of the TRGB position relative to the brightest RGB star is less important because the RGB is well populated. We infer an absolute I-band brightness of M_I=-4.17+/-0.13 mag for the TRGB compared with the theoretical prediction of -3.99+/-0.07 mag, in reasonable agreement with each other. A significant brightness increase caused by neutrino dipole moments is constrained such that mu_nu, 17 pages, 20 figures, accepted for publication in Astronomy and Astrophysics

If axions or other low-mass pseudoscalars couple to electrons (``fine structure constant'' $\alpha_a$) they are emitted from red giant stars by the Compton process $\gamma+e\to e+a$ and by bremsstrahlung $e+(Z,A)\to (Z,A)+e+a$. We construct a simple analytic expression for the energy-loss rate for all conditions relevant for a red giant and include axion losses in evolutionary calculations from the main sequence to the helium flash. We find that $\alpha_a\lapprox0.5\mn(-26)$ or $m_a\lapprox 9\,\meV/\cos^2\beta$ lest the red giant core at helium ignition exceed its standard mass by more than $0.025\,\MM_\odot$, in conflict with observational evidence. Our bound is the most restrictive limit on $\alpha_a$, but it does not exclude the possibility that axion emission contributes significantly to the cooling of ZZ~Ceti stars such as G117--B15A for which the period decrease was recently measured., Comment: 11 pages, uuencoded and compressed postscript file

Accurately determining the properties of stars is of prime importance for characterizing stellar populations in our Galaxy. The field of asteroseismology has been thought to be particularly successful in such an endeavor for stars in different evolutionary stages. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is mandatory. With this purpose, we present a new technique to obtain stellar properties by coupling asteroseismic analysis with the InfraRed Flux Method. By using two global seismic observables and multi-band photometry, the technique allows us to obtain masses, radii, effective temperatures, bolometric fluxes, and hence distances for field stars in a self-consistent manner. We apply our method to 22 solar-like oscillators in the Kepler short-cadence sample, that have accurate Hipparcos parallaxes. Our distance determinations agree to better than 5%, while measurements of spectroscopic effective temperatures and interferometric radii also validate our results. We briefly discuss the potential of our technique for stellar population analysis and models of Galactic Chemical Evolution., Comment: 28 pages, 5 figures, ApJ, accepted

We present secure [NII[ detections in two mm-bright, strongly lensed objects at high redshift, APM08279+5255 (z=3.911) and MM18423+5938 (z=3.930), using the IRAM Plateau de Bure Interferometer. Due to its ionization energy [NII] is a good tracer of the ionized gas phase in the interstellar medium. The measured fluxes are S([NII])=(4.8+/-0.8) Jy km/s and (7.4+/-0.5) Jy km/s respectively, yielding line luminosities of L([NII]) =(1.8+/-0.3) x 10^9 \mu^{-1} Lsun for APM08279+5255 and L([NII]) =(2.8+/-0.2) x 10^9 \mu^{-1} Lsun for MM18423+5938. Our high-resolution map of the [NII] and 1 mm continuum emission in MM18423+5938 clearly resolves an Einstein ring in this source, and reveals a velocity gradient in the dynamics of the ionized gas. A comparison of these maps with high-resolution EVLA CO observations enables us to perform the first spatially-resolved study of the dust continuum-to-molecular gas surface brightness (Sigma_{FIR} Sigma_{CO}^N, which can be interpreted as the star formation law) in a high-redshift object. We find a steep relation (N=1.4+/-0.2), consistent with a starbursting environment. We measure a [NII]/FIR luminosity ratio in APM0828+5255 and MM18423+5938 of 9.0 x 10^{-6} and 5.8 x 10^{-6}, respectively. This is in agreement with the decrease of the [NII]/FIR ratio at high FIR luminosities observed in local galaxies., Comment: 5 Figures, 1 Table. Accepted for publication in ApJ

We have calculated synthetic spectra for typical chemical element mixtures (i.e., a standard alpha-enhanced distribution, and distributions displaying CN and ONa anticorrelations) found in the various subpopulations harboured by Galactic globular clusters. From the spectra we have determined bolometric corrections to the standard Johnson-Cousins and Stroemgren filters, and finally predicted colours. These bolometric corrections and colour-transformations, coupled to our theoretical isochrones with the appropriate chemical composition, provide a complete and self-consistent set of theoretical predictions for the effect of abundance variations on the observed cluster CMD. CNO abundance variations affect mainly wavelengths shorter than 400 nm, due to the arise of molecular absorption bands in cooler atmospheres. As a consequence, colour and magnitude changes are largest in the blue filters, independently of using broad or intermediate bandpasses. Colour-magnitude diagrams involving uvy and UB filters (and their various possible colour combinations) are thus the ones best suited to infer photometrically the presence of multiple stellar generations in individual clusters. They are particularly sensitive to variations in the N abundance, with the largest variations affecting the Red Giant Branch (RGB) and lower Main Sequence (MS). BVI diagrams are expected to display multiple sequences only if the different populations are characterized by variations of the C+N+O sum and helium abundance, that lead to changes in luminosity and effective temperature, but leave the flux distribution above 400 nm practically unaffected. A variation of just the helium abundance, up to the level we investigate here, affects exclusively the interior structure of stars, and is largely irrelevant for the atmospheric structure and the resulting flux distribution in the whole wavelength range spanned by our analysis., 15 pages, 15 figures, submitted to A&A, referee comments addressed

We determined the age of the stellar content of the Galactic halo by considering main-sequence turn-off stars. From the large number of halo stars provided by Sloan Digital Sky Survey, we could accurately detect the turn-off as a function of metallicity of the youngest dominant population, which was done by looking at the hottest (bluest) stars of a population. Using the turn-off temperature of a population of a given metallicity, we looked for the isochrones with that turn-off temperature and metallicity and found no age gradient as a function of metallicity. This would mean that this dominating population of the Galactic halo formed rapidly, probably during the collapse of the proto-Galactic gas. Moreover, we could find a significant number of stars with hotter temperatures than the turn-off, which might be blue horizontal branch (BHB) stars, blue stragglers, or main sequence stars that are younger than the dominant population and were probably formed in external galaxies and accreted later on to our Milky Way. Motivated by the current debate about the efficiency of gravitational settling (atomic diffusion) in the interior of old solar-type stars, we used isochrones with and without settling to determine the ages. When ignoring diffusion in the isochrones we obtained ages of 14-16 Gyr. This result is a strong argument against inhibited diffusion in old halo field stars, since it results in a serious conflict with the age of the Universe of 13.7 Gyr. The age obtained including diffusion in the isochrones was 10-12 Gyr, which agrees with the absolute age of the old globular clusters in the inner halo., Comment: Astronomy and Astrophysics -- in press

We have measured solar-like oscillations in red giants using time-series photometry from the first 34 days of science operations of the Kepler Mission. The light curves, obtained with 30-minute sampling, reveal clear oscillations in a large sample of G and K giants, extending in luminosity from the red clump down to the bottom of the giant branch. We confirm a strong correlation between the large separation of the oscillations (Delta nu) and the frequency of maximum power (nu_max). We focus on a sample of 50 low-luminosity stars (nu_max > 100 muHz, L, Comment: accepted by ApJ Letters, to appear in special Kepler issue. Updated references

Asteroseismology of stars in clusters has been a long-sought goal because the assumption of a common age, distance and initial chemical composition allows strong tests of the theory of stellar evolution. We report results from the first 34 days of science data from the Kepler Mission for the open cluster NGC 6819 -- one of four clusters in the field of view. We obtain the first clear detections of solar-like oscillations in the cluster red giants and are able to measure the large frequency separation and the frequency of maximum oscillation power. We find that the asteroseismic parameters allow us to test cluster-membership of the stars, and even with the limited seismic data in hand, we can already identify four possible non-members despite their having a better than 80% membership probability from radial velocity measurements. We are also able to determine the oscillation amplitudes for stars that span about two orders of magnitude in luminosity and find good agreement with the prediction that oscillation amplitudes scale as the luminosity to the power of 0.7. These early results demonstrate the unique potential of asteroseismology of the stellar clusters observed by Kepler., Comment: 5 pages, 4 figures, accepted by ApJ (Lett.)

We report on a successful, simultaneous observation and modelling of the millimeter (mm) to near-infrared (NIR) flare emission of the Sgr A* counterpart associated with the supermassive black hole at the Galactic centre (GC). We present a mm/sub-mm light curve of Sgr A* with one of the highest quality continuous time coverages and study and model the physical processes giving rise to the variable emission of Sgr A*., Comment: 14 pages, 16 figures

We describe and discuss hydrodynamic simulations of the core helium flash using an initial model of a 1.25 M_sol star with a metallicity of 0.02 near at its peak. Past research concerned with the dynamics of the core helium flash is inconclusive. Its results range from a confirmation of the standard picture, where the star remains in hydrostatic equilibrium during the flash (Deupree 1996), to a disruption or a significant mass loss of the star (Edwards 1969; Cole & Deupree 1980). However, the most recent multidimensional hydrodynamic study (Dearborn 2006) suggests a quiescent behavior of the core helium flash and seems to rule out an explosive scenario. Here we present partial results of a new comprehensive study of the core helium flash, which seem to confirm this qualitative behavior and give a better insight into operation of the convection zone powered by helium burning during the flash. The hydrodynamic evolution is followed on a computational grid in spherical coordinates using our new version of the multi-dimensional hydrodynamic code HERAKLES, which is based on a direct Eulerian implementation of the piecewise parabolic method., 6 pages, 5 figures. IAUS 252 Conference Proceeding (Sanya, China): "The art of modeling stars in the 21st century"

We present a new grid of stellar model calculations for stars on the Asymptotic Giant Branch between 1.0 and 6.0 M_sun. Our grid consists of 5 chemical mixtures between Z=0.0005 and Z=0.04, with both solar-like and $\alpha$-element enhanced metal ratios. We treat consistently the carbon-enhancement of the stellar envelopes by using opacity tables with varying C/O-ratio and by employing theoretical mass loss rates for carbon stars. The low temperature opacities have been calculated specifically for this project. For oxygen stars we use an empirical mass loss formalism. The third dredge-up is naturally obtained by including convective overshooting. Our models reach effective temperatures in agreement with earlier synthetic models, which included approximative carbon-enriched molecular opacities and show good agreement with empirically determined carbon-star lifetimes. A fraction of the models could be followed into the post-AGB phase, for which we provide models in a mass range supplementing previous post-AGB calculations. Our grid constitutes the most extensive set of AGB-models, calculated with the latest physical input data and treating carbon-enhancement due to the third dredge-up most consistently., Comment: revised version, 34 pages, 17 figures, accepted by A&A

We present 1D numerical simulations aimed at studying the hot-flasher scenario for the formation of He-rich subdwarf stars. Sequences were calculated for a wide range of metallicities and physical assumptions, such as the stellar mass at the moment of the helium core flash. This allows us to study the two previously proposed flavors of the hot-flasher scenario ("deep" and "shallow" mixing cases) and to identify a third transition type. Our sequences are calculated by solving simultaneously the mixing and burning equations within a diffusive convection picture, and in the context of standard mixing length theory. We are able to follow chemical evolution during deep-mixing events in which hydrogen is burned violently, and therefore able to present a homogeneous set of abundances for different metallicities and varieties of hot-flashers. We extend the scope of our work by analyzing the effects of non-standard assumptions, such as the effect of chemical gradients, extra-mixing at convective boundaries, possible reduction in convective velocities, or the interplay between difussion and mass loss. Particular emphasis is placed on the predicted surface properties of the models. We find that the hot-flasher scenario is a viable explanation for the formation and surface properties of He-sdO stars. Our results also show that, during the early He-core burning stage, element diffusion may produce the transformation of (post hot-flasher) He-rich atmospheres into He-deficient ones. If this is so, then we find that He-sdO stars should be the progenitors of some of the hottest sdB stars., Instituto de Astrofísica de La Plata, Facultad de Ciencias Astronómicas y Geofísicas

We study turbulent convection during the core helium flash close to its peak by comparing the results of two and three-dimensional hydrodynamic simulations. We use a multidimensional Eulerian hydrodynamics code based on state-of-the-art numerical techniques to simulate the evolution of the helium core of a $1.25 M_{\odot}$ Pop I star. Our three-dimensional hydrodynamic simulations of the evolution of a star during the peak of the core helium flash do not show any explosive behavior. The convective flow patterns developing in the three-dimensional models are structurally different from those of the corresponding two-dimensional models, and the typical convective velocities are smaller than those found in their two-dimensional counterparts. Three-dimensional models also tend to agree better with the predictions of mixing length theory. Our hydrodynamic simulations show the presence of turbulent entrainment that results in a growth of the convection zone on a dynamic time scale. Contrary to mixing length theory, the outer part of the convection zone is characterized by a sub-adiabatic temperature gradient., 19 pages, 18 figures

We investigate the hydrodynamics of the core helium flash near its peak. Past research concerned with the dynamics of this event is inconclusive. However, the most recent multidimensional hydrodynamic studies suggest a quiescent behavior and seem to rule out an explosive scenario. Previous work indicated, that depending on initial conditions, employed turbulence models, grid resolution, and dimensionality of the simulation, the core helium flash leads either to the disruption of a low-mass star or to a quiescent quasi-hydrostatic evolution. We try to clarify this issue by simulating the evolution with advanced numerical methods and detailed microphysics. Assuming spherical or axial symmetry, we simulate the evolution of the helium core of a $1.25 M_{\odot}$ star with a metallicity Z=0.02 during the core helium flash at its peak with a grid-based hydrodynamics code. We find that the core helium flash neither rips the star apart, nor that it significantly alters its structure, as convection plays a crucial role in keeping the star in hydrostatic equilibrium. In addition, our simulations show the presence of overshooting, which implies new predictions concerning mixing of chemical species in red giants., 13 pages, 23 figures