The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Philip Massey - One of the best experts on this subject based on the ideXlab platform.
-
betelgeuse just isn t that cool Effective Temperature alone cannot explain the recent dimming of betelgeuse
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Emily M Levesque, Philip MasseyAbstract:We present optical spectrophotometry of the red supergiant Betelgeuse from 2020 February 15, during its recent unprecedented dimming episode. By comparing this spectrum to stellar atmosphere models for cool supergiants, as well as spectrophotometry of other Milky Way red supergiants, we conclude that Betelgeuse has a current Effective Temperature of 3600 +/- 25 K. While this is slightly cooler than previous measurements taken prior to Betelgeuse's recent lightcurve evolution, this drop in Effective Temperature is insufficient to explain Betelgeuse's recent optical dimming. We propose that episodic mass loss and an increase in the amount of large-grain circumstellar dust along our sightline to Betelgeuse is the most likely explanation for its recent photometric evolution.
-
The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought
The Astrophysical Journal, 2005Co-Authors: Emily M Levesque, Philip Massey, B Plez, E Josselin, Andre Maeder, K. A. G. Olsen, Georges MeynetAbstract:We use moderate-resolution optical spectrophotometry and the new MARCS stellar atmosphere models to determine the Effective Temperatures of 74 Galactic red supergiants (RSGs). The stars are mostly members of OB associations or clusters with known distances, allowing a critical comparison with modern stellar evolutionary tracks. We find we can achieve excellent matches between the observations and the reddened model fluxes and molecular transitions, although the atomic lines Ca I ?4226 and Ca II H and K are found to be unrealistically strong in the models. Our new Effective Temperature scale is significantly warmer than those in the literature, with the differences amounting to 400 K for the latest type M supergiants (i.e., M5 I). We show that the newly derived Temperatures and bolometric corrections give much better agreement with stellar evolutionary tracks. This agreement provides a completely independent verification of our new Temperature scale. The combination of Effective Temperature and bolometric luminosities allows us to calculate stellar radii; the coolest and most luminous stars (KW Sgr, Case 75, KY Cyg, HD 206936=? Cep) have radii of roughly 1500 Rsolar (7 AU), in excellent accordance with the largest stellar radii predicted from current evolutionary theory, although smaller than that found by others for the binary VV Cep and for the peculiar star VY CMa. We find that similar results are obtained for the Effective Temperatures and bolometric luminosities using only the dereddened V-K colors, providing a powerful demonstration of the self-consistency of the MARCS models.
-
the physical properties and Effective Temperature scale of o type stars as a function of metallicity ii analysis of 20 more magellanic cloud stars and results from the complete sample
The Astrophysical Journal, 2005Co-Authors: Philip Massey, J Puls, A W A Pauldrach, Fabio Bresolin, Rolf P Kudritzki, T SimonAbstract:In order to determine the physical properties of the hottest and most luminous stars and understand how these properties change as a function of metallicity, we have analyzed HST/UV and high-S/N optical spectra of an additional 20 Magellanic Cloud stars, doubling the sample presented in the first paper in this series. Our analysis uses non-LTE line-blanketed models that include spherical extension and the hydrodynamics of the stellar wind. In addition, our data set includes FUSE observations of O VI and HST near-UV He I and He II lines to test for consistency of our derived stellar properties for a few stars. The results from the complete sample are as follows: (1) We present an Effective Temperature scale for O stars as a function of metallicity. We find that the SMC O3-7 dwarfs are 4000 K hotter than Galactic stars of the same spectral type. The difference is in the sense expected due to the decreased significance of line blanketing and wind blanketing at the lower metallicities that characterize the SMC. The Temperature difference between the SMC and Milky Way O dwarfs decreases with decreasing Temperature, becoming negligible by spectral type B0, in accord with the decreased effects of stellar winds at lower Temperatures and luminosities. The Temperatures of the LMC stars appear to be intermediate between that of the Milky Way and SMC, as expected based on their metallicities. Supergiants show a similar effect but are roughly 3000-4000 K cooler than dwarfs for early O stars, also with a negligible difference by B0. The giants appear to have the same Effective Temperature scale as dwarfs, consistent with there being little difference in the surface gravities. When we compare our scale to other recent modeling efforts, we find good agreement with some CMFGEN results, while other CMFGEN studies are discordant, although there are few individual stars in common. WM-BASIC modeling by others has resulted in significantly cooler Effective Temperatures than what we find, as does the recent TLUSTY/CMFGEN study of stars in the NGC 346 cluster, but our results lead to a far more coeval placement of stars in the H-R diagram for this cluster. (2) We find that the wind momentum of these stars scales with luminosity and metallicity in the ways predicted by radiatively driven wind theory, supporting the use of photospheric analyses of hot luminous stars as a distance indicator for galaxies with resolved massive star populations. (3) A comparison of the spectroscopic masses with those derived from stellar evolutionary theory shows relatively good agreement for stars with Effective Temperatures below 45,000 K; however, stars with higher Temperatures all show a significant mass discrepancy, with the spectroscopic masses a factor of 2 or more smaller than the evolutionary masses. This problem may in part be due to unrecognized binaries in our sample, but the result suggests a possible systematic problem with the surface gravities or stellar radii derived from our models. (4) Our sample contains a large number of stars of the earliest O types, including those of the newly proposed O2 subtype. We provide the first quantitative descriptions of their defining spectral characteristics and investigate whether the new types are a legitimate extension of the Effective Temperature sequence. We find that the N III/N IV emission line ratio used to define the new classes does not, by itself, serve as an Effective Temperature indicator within a given luminosity class: there are O3.5 V stars that are as hot or hotter than O2 V stars. However, the He I/He II ratio does not fair much better for stars this hot, as we find that He I λ4471/He II λ4542, usually taken primarily as a Temperature indicator, becomes sensitive to both the mass-loss rate and surface gravities for the hottest stars. This emphasizes the need to rely on all of the spectroscopic diagnostic lines, and not simply N III/N IV or even He I/He II, for these extreme objects. (5) The two stars with the most discordant radial velocities in our sample happen to be O3 field stars, i.e., found far from the nearest OB associations. This provides the first compelling observational evidence as to the origin of the field O stars in the Magellanic Clouds, i.e., that these are classic runaway OB stars, ejected from their birthplaces.
-
the Effective Temperature scale of galactic red supergiants cool but not as cool as we thought
arXiv: Astrophysics, 2005Co-Authors: Emily M Levesque, Philip Massey, K Olsen, B Plez, E Josselin, Andre Maeder, Georges MeynetAbstract:We use moderate-resolution optical spectrophotometry and the new MARCS stellar atmosphere models to determine the Effective Temperatures of 74 Galactic red supergiants. From these we find a new Effective Temperature scale that is significantly warmer than those in the literature. We show that this Temperature scale, along with the newly derived bolometric corrections, gives much better agreement between our red supergiants and stellar evolutionary tracks. This agreement provides an independent verification of our new Temperature scale. The combination of Effective Temperature and bolometric luminosities allows us to calculate stellar radii; the coolest and most luminous stars have radii of roughly 1500 solar radii (7 AU), in excellent accordance with the largest stellar radii predicted from current evolutionary theory. We find that similar results are obtained for the Effective Temperatures and bolometric luminosities using only the de-reddened V-K colors, providing a powerful demonstration of the self-consistency of the MARCS models.
-
the physical properties and Effective Temperature scale of o type stars as a function of metallicity ii analysis of 20 more magellanic cloud stars and results from the complete sample
arXiv: Astrophysics, 2005Co-Authors: Philip Massey, J Puls, A W A Pauldrach, Fabio Bresolin, Rolf P Kudritzki, T SimonAbstract:We analyze the optical and UV spectra of an additional sample of 20 Magellanic Cloud O stars, and draw conclusions from the complete sample of 40 stars. We find (1) The SMC O3-7 dwarfs are about 4000 K cooler than their Galactic counterparts; this is in the sense expected from the decreased signficiance of line-blanketing and wind-blanketing at lower metallicities. The difference decreases with later types, becoming negligible by B0 V. A similar difference is found for the supergiants. (2) The wind momentum of these stars scales with luminosity and metallicty in the ways predicted by radiatively-driven wind theory. (3) A comparison of the masses derived from spectroscopy with those derived from stellar evolutionary theory shows a significant discrepancy for stars hotter than 45000, although good agreement is found for cooler stars. (4) For the hottest O stars (O2-3.5) neither the NIII/NIV ratio, nor even the HeI/HeII ratio, does a good job of predicting the Effective Temperature by itself. Instead, a full analysis is needed to derive physical parameters. Thus there are O3.5V stars which are as hot or hotter than stars classified as O2V. (5) The two stars with the most discordant radial velocities in our sample happen to be O3 "field stars". This provides the first compelling observational evidence that the "field" O stars in the Magellanic Clouds may be runaway OB stars, ejected from their birth place.
H Bruntt - One of the best experts on this subject based on the ideXlab platform.
-
a revised Effective Temperature scale for the kepler input catalog
Astrophysical Journal Supplement Series, 2012Co-Authors: Marc H Pinsonneault, J Molendażakowicz, W J Chaplin, T S Metcalfe, H BrunttAbstract:We present a catalog of revised Effective Temperatures for stars observed in long-cadence mode in the Kepler Input Catalog (KIC). We use Sloan Digital Sky Survey (SDSS) griz filters tied to the fundamental Temperature scale. Polynomials for griz color-Temperature relations are presented, along with correction terms for surface gravity effects, metallicity, and statistical corrections for binary companions or blending. We compare our Temperature scale to the published infrared flux method (IRFM) scale for VTJKs in both open clusters and the Kepler fields. We find good agreement overall, with some deviations between (J ? Ks )-based Temperatures from the IRFM and both SDSS filter and other diagnostic IRFM color-Temperature relationships above 6000?K. For field dwarfs, we find a mean shift toward hotter Temperatures relative to the KIC, of order 215?K, in the regime where the IRFM scale is well defined (4000?K to 6500?K). This change is of comparable magnitude in both color systems and in spectroscopy for stars with T eff below 6000?K. Systematic differences between Temperature estimators appear for hotter stars, and we define corrections to put the SDSS Temperatures on the IRFM scale for them. When the theoretical dependence on gravity is accounted for, we find a similar Temperature scale offset between the fundamental and KIC scales for giants. We demonstrate that statistical corrections to color-based Temperatures from binaries are significant. Typical errors, mostly from uncertainties in extinction, are of order 100?K. Implications for other applications of the KIC are discussed.
-
a revised Effective Temperature scale for the kepler input catalog
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Marc H Pinsonneault, J Molendażakowicz, W J Chaplin, T S Metcalfe, H BrunttAbstract:We present a catalog of revised Effective Temperatures for stars observed in long-cadence mode in the Kepler Input Catalog (KIC). We use SDSS griz filters tied to the fundamental Temperature scale. Polynomials for griz color-Temperature relations are presented, along with correction terms for surface gravity effects, metallicity, and statistical corrections for binary companions or blending. We compare our Temperature scale to the published infrared flux method (IRFM) scale for VJKs in both open clusters and the Kepler fields. We find good agreement overall, with some deviations between (J - Ks)-based Temperatures from the IRFM and both SDSS filter and other diagnostic IRFM color-Temperature relationships above 6000 K. For field dwarfs we find a mean shift towards hotter Temperatures relative to the KIC, of order 215 K, in the regime where the IRFM scale is well-defined (4000 K to 6500 K). This change is of comparable magnitude in both color systems and in spectroscopy for stars with Teff below 6000 K. Systematic differences between Temperature estimators appear for hotter stars, and we define corrections to put the SDSS Temperatures on the IRFM scale for them. When the theoretical dependence on gravity is accounted for we find a similar Temperature scale offset between the fundamental and KIC scales for giants. We demonstrate that statistical corrections to color-based Temperatures from binaries are significant. Typical errors, mostly from uncertainties in extinction, are of order 100 K. Implications for other applications of the KIC are discussed.
-
the radius and Effective Temperature of the binary ap star β crb from chara fluor and vlt naco observations
Astronomy and Astrophysics, 2010Co-Authors: H Bruntt, P Kervella, A Merand, I M Brandao, T R Bedding, Ten T Brummelaar, Coude V Du Foresto, M S Cunha, C FarringtonAbstract:Context. The prospects for using the asteroseismology of rapidly oscillating Ap (roAp) stars are hampered by the large uncertainty in fundamental stellar parameters. Results in the literature for the Effective Temperature (Teff) often span a range of 1000 K. Aims. Our goal is to reduce systematic errors and improve the Teff calibration of Ap stars based on new interferometric measurements. Methods. We obtained long-baseline interferometric observations of β CrB using the CHARA/FLUOR instrument. To disentangle the flux contributions of the two components of this binary star, we obtained VLT/NACO adaptive optics images. Results. We determined limb-darkened angular diameters of 0.699 ± 0.017 mas for β CrB A (from interferometry) and 0.415 ± 0.017 mas for β CrB B (from surface brightness-colour relations), corresponding to radii of 2.63 ± 0.09 R� (3.4% uncertainty) and 1.56 ± 0.07 R� (4.5%). The combined bolometric flux of the A+B components was determined from satellite UV data, spectrophotometry in the visible, and broadband data in the infrared. The flux from the B component constitutes 16 ± 4% of the total flux and was determined by fitting an ATLAS9 model atmosphere to the broad-band NACO J and K magnitudes. By combining the flux of the A component with its measured angular diameter, we determined the Effective Temperature Teff (A) = 7980 ± 180 K (2.3%). Conclusions. Our new interferometric and imaging data enable nearly model-independent determination of the Effective Temperature of β CrB A. Including our recent study of α Cir, we now have direct Teff measurements of two of the brightest roAp stars, providing a strong benchmark for improved calibration of the Teff scale for Ap stars. This will support the use of potentially strong constraints imposed by asteroseismic studies of roAp stars.
Jorge Melendez - One of the best experts on this subject based on the ideXlab platform.
-
an absolutely calibrated Effective Temperature scale from the infrared flux method
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: L Casagrande, Jorge Melendez, I Ramirez, M S Bessell, Martin AsplundAbstract:Various Effective Temperature scales have been proposed over the years. Despite much work and the high internal precision usually achieved, systematic differences of order 100 K (or more) among various scales are still present. We present an investigation based on the Infrared Flux Method aimed at assessing the source of such discrepancies and pin down their origin. We break the impasse among different scales by using a large set of solar twins, stars which are spectroscopically and photometrically identical to the Sun, to set the absolute zero point of the Effective Temperature scale to within few degrees. Our newly calibrated, accurate and precise Temperature scale applies to dwarfs and subgiants, from super-solar metallicities to the most metal-poor stars currently known. At solar metallicities our results validate spectroscopic Effective Temperature scales, whereas for [Fe/H]<-2.5 our Temperatures are roughly 100 K hotter than those determined from model fits to the Balmer lines and 200 K hotter than those obtained from the excitation equilibrium of Fe lines. Empirical bolometric corrections and useful relations linking photometric indices to Effective Temperatures and angular diameters have been derived. Our results take full advantage of the high accuracy reached in absolute calibration in recent years and are further validated by interferometric angular diameters and space based spectrophotometry over a wide range of Effective Temperatures and metallicities.
-
The Effective Temperature Scale of FGK Stars. II. Teff:Color:[Fe/H] Calibrations
The Astrophysical Journal, 2005Co-Authors: Ivan Ramirez, Jorge MelendezAbstract:We present up-to-date metallicity-dependent Temperature versus color calibrations for main-sequence and giant stars based on Temperatures derived with the infrared flux method (IRFM). Seventeen colors in the photometric systems UBV, uvby, Vilnius, Geneva, RI(Cousins), DDO, Hipparcos-Tycho, and Two Micron All Sky Survey (2MASS) have been calibrated. The spectral types covered by the calibrations range from F0 to K5 (7000 K Teff 4000 K) with some relations extending below 4000 K or up to 8000 K. Most of the calibrations are valid in the metallicity range -3.5 [Fe/H] 0.4, although some of them extend to as low as [Fe/H] ~ -4.0. All fits to the data have been performed with more than 100 stars; standard deviations range from 30 to 120 K. Fits were carefully performed and corrected to eliminate the small systematic errors introduced by the calibration formulae. Tables of colors as a function of Teff and [Fe/H] are provided. This work is largely based on the study by A. Alonso and collaborators; thus, our relations do not significantly differ from theirs except for the very metal-poor hot stars. From the calibrations, the Temperatures of 44 dwarf and giant stars with direct Temperatures available are obtained. The comparison with direct Temperatures confirms our finding in Paper I that the zero point of the IRFM Temperature scale is in agreement, to the 10 K level, with the absolute Temperature scale (that based on stellar angular diameters) within the ranges of atmospheric parameters covered by those 44 stars. The colors of the Sun are derived from the present IRFM Teff scale and they compare well with those of five solar analogs. It is shown that if the IRFM Teff scale accurately reproduces the Temperatures of very metal-poor stars, systematic errors of the order of 200 K, introduced by the assumption of (V - K) being completely metallicity independent when studying very metal-poor dwarf stars, are no longer acceptable. Comparisons with other Teff scales, both empirical and theoretical, are also shown to be in reasonable agreement with our results, although it seems that both Kurucz and MARCS synthetic colors fail to predict the detailed metallicity dependence, given that for [Fe/H] = -2.0, differences as high as approximately ±200 K are found.
-
the Effective Temperature scale of fgk stars ii teff color fe h calibrations
arXiv: Astrophysics, 2005Co-Authors: Ivan Ramirez, Jorge MelendezAbstract:We present up-to-date metallicity-dependent Temperature vs. color calibrations for main sequence and giant stars based on Temperatures derived with the infrared flux method (IRFM). Seventeen colors in the following photometric systems: UBV, uvby, Vilnius, Geneva, RI(Cousins), DDO, Hipparcos-Tycho, and 2MASS, have been calibrated. The spectral types covered range from F0 to K5 (7000 K
T M Kojima - One of the best experts on this subject based on the ideXlab platform.
-
stepwise formation of h3o h2o n in an ion drift tube empirical Effective Temperature of association dissociation reaction equilibrium in an electric field
Journal of Chemical Physics, 2016Co-Authors: Y Nakai, Naoki Watanabe, H Hidaka, T M KojimaAbstract:We measured equilibrium constants for H3O+(H2O)n−1 + H2O↔H3O+(H2O)n (n = 4–9) reactions taking place in an ion drift tube with various applied electric fields at gas Temperatures of 238–330 K. The zero-field reaction equilibrium constants were determined by extrapolation of those obtained at non-zero electric fields. From the zero-field reaction equilibrium constants, the standard enthalpy and entropy changes, ΔHn,n−10 and ΔSn,n−10, of stepwise association for n = 4–8 were derived and were in reasonable agreement with those measured in previous studies. We also examined the electric field dependence of the reaction equilibrium constants at non-zero electric fields for n = 4–8. An Effective Temperature for the reaction equilibrium constants at non-zero electric field was empirically obtained using a parameter describing the electric field dependence of the reaction equilibrium constants. Furthermore, the size dependence of the parameter was thought to reflect the evolution of the hydrogen-bond structure of...
-
stepwise formation of h3o h2o n in an ion drift tube empirical Effective Temperature of association dissociation reaction equilibrium in an electric field
Journal of Chemical Physics, 2016Co-Authors: Y Nakai, Naoki Watanabe, H Hidaka, T M KojimaAbstract:We measured equilibrium constants for H3O(+)(H2O)n-1 + H2O↔H3O(+)(H2O)n (n = 4-9) reactions taking place in an ion drift tube with various applied electric fields at gas Temperatures of 238-330 K. The zero-field reaction equilibrium constants were determined by extrapolation of those obtained at non-zero electric fields. From the zero-field reaction equilibrium constants, the standard enthalpy and entropy changes, ΔHn,n-1 (0) and ΔSn,n-1 (0), of stepwise association for n = 4-8 were derived and were in reasonable agreement with those measured in previous studies. We also examined the electric field dependence of the reaction equilibrium constants at non-zero electric fields for n = 4-8. An Effective Temperature for the reaction equilibrium constants at non-zero electric field was empirically obtained using a parameter describing the electric field dependence of the reaction equilibrium constants. Furthermore, the size dependence of the parameter was thought to reflect the evolution of the hydrogen-bond structure of H3O(+)(H2O)n with the cluster size. The reflection of structural information in the electric field dependence of the reaction equilibria is particularly noteworthy.
R Lallement - One of the best experts on this subject based on the ideXlab platform.
-
empirical photometric calibration of the gaia red clump colours Effective Temperature and absolute magnitude
Astronomy and Astrophysics, 2018Co-Authors: L Ruizdern, C Babusiaux, F Arenou, C Turon, R LallementAbstract:Context. Gaia Data Release 1 allows the recalibration of standard candles such as the red clump stars. To use those stars, they first need to be accurately characterised. In particular, colours are needed to derive interstellar extinction. As no filter is available for the first Gaia data release and to avoid the atmosphere model mismatch, an empirical calibration is unavoidable. Aims. The purpose of this work is to provide the first complete and robust photometric empirical calibration of the Gaia red clump stars of the solar neighbourhood through colour–colour, Effective Temperature–colour, and absolute magnitude–colour relations from the Gaia , Johnson, 2MASS, Hipparcos, Tycho -2, APASS-SLOAN, and WISE photometric systems, and the APOGEE DR13 spectroscopic Temperatures. Methods. We used a 3D extinction map to select low reddening red giants. To calibrate the colour–colour and the Effective Temperature–colour relations, we developed a MCMC method that accounts for all variable uncertainties and selects the best model for each photometric relation. We estimated the red clump absolute magnitude through the mode of a kernel-based distribution function. Results. We provide 20 colour versus G − K s relations and the first T eff versus G − K s calibration. We obtained the red clump absolute magnitudes for 15 photometric bands with, in particular, M K s = (−1.606 ± 0.009) and M G = (0.495 ± 0.009) + (1.121 ± 0.128)( G − K s −2.1). We present a dereddened Gaia -TGAS HR diagram and use the calibrations to compare its red clump and its red giant branch bump with Padova isochrones.
-
empirical photometric calibration of the gaia red clump colours Effective Temperature and absolute magnitude
arXiv: Solar and Stellar Astrophysics, 2017Co-Authors: L Ruizdern, C Babusiaux, F Arenou, C Turon, R LallementAbstract:Gaia Data Release 1 allows to recalibrate standard candles such as the Red Clump stars. To use those, they first need to be accurately characterised. In particular, colours are needed to derive the interstellar extinction. As no filter is available for the first Gaia data release and to avoid the atmosphere model mismatch, an empirical calibration is unavoidable. The purpose of this work is to provide the first complete and robust photometric empirical calibration of the Gaia Red Clump stars of the solar neighbourhood, through colour-colour, Effective Temperature-colour and absolute magnitude-colour relations, from the Gaia, Johnson, 2MASS, Hipparcos, Tycho-2, APASS-SLOAN and WISE photometric systems, and the APOGEE DR13 spectroscopic Temperatures. We used a 3D extinction map to select low reddening red giants. To calibrate the colour-colour and the Effective Temperature-colour relations, we developed a MCMC method which accounts for all variable uncertainties and selects the best model for each photometric relation. We estimate the Red Clump absolute magnitude through the mode of a kernel-based distribution function. We provide 20 colour vs G-Ks relations and the first Teff vs G-Ks calibration. We obtained the Red Clump absolute magnitudes for 15 photometric bands with, in particular, M_Ks = -1.606 +/- 0.009 and M_G = (0.495 +/- 0.009) + (1.121 +/- 0.128) (G-Ks-2.1). We present an unreddened Gaia-TGAS HR diagram and use the calibrations to compare its Red Clump and its Red Giant Branch Bump with the Padova isochrones.
