- ID:
- ivo://CDS.VizieR/J/ApJ/779/188
- Title:
- Spectra of nearby late K and M Kepler stars
- Short Name:
- J/ApJ/779/188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use moderate-resolution spectra of nearby late K and M dwarf stars with parallaxes and interferometrically determined radii to refine their effective temperatures, luminosities, and metallicities. We use these revised values to calibrate spectroscopic techniques to infer the fundamental parameters of more distant late-type dwarf stars. We demonstrate that, after masking out poorly modeled regions, the newest version of the PHOENIX atmosphere models accurately reproduce temperatures derived bolometrically. We apply methods to late-type hosts of transiting planet candidates in the Kepler field, and calculate effective temperature, radius, mass, and luminosity with typical errors of 57K, 7%, 11%, and 13%, respectively. We find systematic offsets between our values and those from previous analyses of the same stars, which we attribute to differences in atmospheric models utilized for each study. We investigate which of the planets in this sample are likely to orbit in the circumstellar habitable zone. We determine that four candidate planets (KOI 854.01, 1298.02, 1686.01, and 2992.01) are inside of or within 1{sigma} of a conservative definition of the habitable zone, but that several planets identified by previous analyses are not (e.g., KOI 1422.02 and KOI 2626.01). Only one of the four habitable-zone planets is Earth sized, suggesting a downward revision in the occurrence of such planets around M dwarfs. These findings highlight the importance of measuring accurate stellar parameters when deriving parameters of their orbiting planets.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/547/A91
- Title:
- Spectroscopic analysis of 348 red giants
- Short Name:
- J/A+A/547/A91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present basic atmospheric parameters (Teff, logg, vt, and [Fe/H]) as well as luminosities, masses, radii, and absolute radial velocities for 348 stars, presumably giants, from the ~1000 star sample observed within the Penn State-Torun Centre for Astronomy Planet Search (PTPS) with the High Resolution Spectrograph of the 9.2m Hobby-Eberly Telescope. The stellar parameters (luminosities, masses, radii) are key to properly interpreting newly discovered low-mass companions, while a systematic study of the complete sample will create a basis for future statistical considerations concerning the appearance of low-mass companions around evolved low- and intermediate-mass stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/848/11
- Title:
- Spectroscopic and photometric analysis of WDs
- Short Name:
- J/ApJ/848/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed spectroscopic and photometric analysis of 219 DA and DB white dwarfs for which trigonometric parallax measurements are available. Our aim is to compare the physical parameters derived from the spectroscopic and photometric techniques, and then to test the theoretical mass-radius relation for white dwarfs using these results. The agreement between spectroscopic and photometric parameters is found to be excellent, especially for effective temperatures, showing that our model atmospheres and fitting procedures provide an accurate, internally consistent analysis. The values of surface gravity and solid angle obtained, respectively, from spectroscopy and photometry, are combined with parallax measurements in various ways to study the validity of the mass-radius relation from an empirical point of view. After a thorough examination of our results, we find that 73% and 92% of the white dwarfs are consistent within 1{sigma} and 2{sigma} confidence levels, respectively, with the predictions of the mass-radius relation, thus providing strong support to the theory of stellar degeneracy. Our analysis also allows us to identify 15 stars that are better interpreted in terms of unresolved double degenerate binaries. Atmospheric parameters for both components in these binary systems are obtained using a novel approach. We further identify a few white dwarfs that are possibly composed of an iron core rather than a carbon/oxygen core, since they are consistent with Fe-core evolutionary models.
- ID:
- ivo://CDS.VizieR/J/ApJ/868/57
- Title:
- Spectroscopic HR diagram of OB stars in the SMC
- Short Name:
- J/ApJ/868/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive stellar atmosphere analysis of 329 O- and B-type stars in the Small Magellanic Cloud (SMC) from the RIOTS4 survey. Using spectroscopically derived effective temperature Teff and surface gravities, we find that classical Be stars appear misplaced to low Teff and high luminosity in the spectroscopic Hertzsprung-Russell diagram (sHRD). Together with the most luminous stars in our sample, the stellar masses derived from the sHRD for these objects are systematically larger than those obtained from the conventional Hertzsprung-Russell diagram. This suggests that the well-known, spectroscopic mass-discrepancy problem may be linked to the fact that both groups of stars have outer envelopes that are nearly gravitationally unbound. The non-emission-line stars in our sample mainly appear on the main sequence, allowing a first estimate of the terminal-age main sequence (TAMS) in the SMC, which matches the predicted TAMS between 12 and 40M_{sun}_ at SMC metallicity. We further find a large underabundance of stars above ~25M_{sun}_ near the zero-age main sequence, reminiscent of such earlier findings in the Milky Way and Large Magellanic Cloud.
- ID:
- ivo://CDS.VizieR/J/AJ/156/117
- Title:
- Spectroscopic orbits for late-type stars. II.
- Short Name:
- J/AJ/156/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined spectroscopic orbital elements for 13 systems - 10 single-lined binaries and three double-lined binaries. For the three binaries with previously published spectroscopic orbits, we have computed improved or comparable elements. While two systems have relatively short periods between 10 and 19 days, the remaining systems have much longer periods ranging from 604 to 9669 days. One of the single-lined systems, HD 142640, shows both short-period and long-period velocity variations and so is triple. For three systems - HD 59380, HD 160933, and HD 161163 - we have combined our spectroscopic results with Hipparcos astrometric observations to obtain astrometric orbits. For HD 14802 we have determined a joint orbital solution from spectroscopic velocities and interferometric observations. The orbits given here will be useful in combination with future interferometric and Gaia satellite observations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/397
- Title:
- Spectroscopic study of RGs in the Kepler field
- Short Name:
- J/MNRAS/450/397
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thanks to the recent very high precision photometry of red giants from satellites such as Kepler, precise mass and radius values as well as accurate information of evolutionary stages are already established by asteroseismic approach for a large number of G-K giants. Based on the high-dispersion spectra of selected such 55 red giants in the Kepler field with precisely known seismic parameters (among which parallaxes are available for nine stars), we checked the accuracy of the determination method of stellar parameters previously applied to many red giants by Takeda et al. (2008PASJ...60..781T), since it may be possible to discriminate their complex evolutionary status by using the surface gravity versus mass diagram. We confirmed that our spectroscopic gravity and the seismic gravity satisfactorily agree with each other (to within ~0.1 dex) without any systematic difference. However, the mass values of He-burning red clump giants derived from stellar evolutionary tracks (~2-3 M_{sun}_) were found to be markedly larger by ~50 percent compared to the seismic values (~1-2 M_{sun}_) though such discrepancy is not seen for normal giants in the H-burning phase, which reflects the difficulty of mass determination from intricately overlapping tracks on the luminosity versus effective temperature diagram. This consequence implies that the mass results of many red giants in the clump region determined by Takeda et al. are likely to be significantly overestimated. We also compare our spectroscopically established parameters with recent literature values, and further discuss the prospect of distinguishing the evolutionary status of red giants based on the conventional (i.e. non-seismic) approach.
- ID:
- ivo://CDS.VizieR/J/ApJ/652/681
- Title:
- Spectroscopic subcomponents in multiple systems
- Short Name:
- J/ApJ/652/681
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We propose a methodology for analyzing triple stellar systems that include a visual double star wherein one of the components is a single- or double-lined spectroscopic binary. By using this methodology, we can calculate the most probable values of the spectroscopic binary's inclination, the angular separation between its components, and its stellar masses, and we can even estimate the spectral types. For a few W UMa-type eclipsing binaries, stellar radii are also determined. Moreover, we present new formulae for calculating stellar masses depending on spectral type. In this way we have studied 61 triple systems, five of them W UMatype eclipsing binaries with low-mass subcomponents. In addition, we study nine quadruple systems, applying the same methodology and considering them twice as a triple system.
- ID:
- ivo://CDS.VizieR/J/ApJ/834/176
- Title:
- Spectroscopic survey of M37 candidate members
- Short Name:
- J/ApJ/834/176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a spectroscopic survey to characterize chromospheric activity, as measured by H{alpha} emission, in low-mass members of the 500Myr old open cluster M37. Combining our new measurements of H{alpha} luminosities (L_H{alpha}_) with previously cataloged stellar properties, we identify saturated and unsaturated regimes in the dependence of the L_H{alpha}_-to-bolometric luminosity ratio, L_H{alpha}_/L_bol_, on the Rossby number R_o_. All rotators with R_o_ smaller than 0.03+/-0.01 converge to an activity level of L_H{alpha}_/L_bol_=(1.27+/-0.02)x10^-4^. This saturation threshold (R_o,sat_=0.03+/-0.01) is statistically smaller than that found in most studies of the rotation-activity relation. In the unsaturated regime, slower rotators have lower levels of chromospheric activity, with L_H{alpha}_/L_bol_(R_o_) following a power-law of index {beta}=-0.51+/-0.02, slightly shallower than that found for a combined ~650Myr old sample of Hyades and Praesepe stars. By comparing this unsaturated behavior to that previously found for coronal activity in M37 (as measured via the X-ray luminosity, L_X_), we confirm that chromospheric activity decays at a much slower rate than coronal activity with increasing R_o_. While a comparison of L_H{alpha}_ and L_X_ for M37 members with measurements of both reveals a nearly 1:1 relation, removing the mass-dependencies by comparing instead L_H{alpha}_/L_bol_ and L_X_/L_bol_ does not provide clear evidence for such a relation. Finally, we find that R_o,sat_ is smaller for our chromospheric than for our coronal indicator of activity (R_o,sat_=0.03+/-0.01 versus 0.09+/-0.01). We interpret this as possible evidence for coronal stripping.
- ID:
- ivo://CDS.VizieR/J/ApJ/700/1216
- Title:
- Spectroscopy of Be stars in open clusters
- Short Name:
- J/ApJ/700/1216
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We recently discovered a large number of highly active Be stars in the open cluster NGC 3766, making it an excellent location to study the formation mechanism of Be star disks. To explore whether similar disk appearances and/or disappearances are common among the Be stars in other open clusters, we present here multiple epochs of H{alpha} spectroscopy for 296 stars in eight open clusters. We identify 12 new transient Be stars and confirm 17 additional Be stars with relatively stable disks. By comparing the H{alpha} equivalent widths to the photometric y-H{alpha} colors, we present a method to estimate the strength of the H{alpha} emission when spectroscopy is not available. For a subset of 128 stars in four open clusters, we also use blue optical spectroscopy and available Stromgren photometry to measure their projected rotational velocities, effective temperatures, and polar surface gravities. We combine our Be star detections from these four clusters to investigate physical differences between the transient Be stars, stable Be stars, and normal B-type stars with no line emission. Both types of Be stars are faster rotating populations than normal B-type stars, and we find no significant physical differences between the transient and stable Be stars in our sample.
- ID:
- ivo://CDS.VizieR/J/AJ/152/40
- Title:
- Spectroscopy of 341 bright A- and B-type stars
- Short Name:
- J/AJ/152/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Binary stars and higher-order multiple systems are a ubiquitous outcome of star formation, especially as the system mass increases. The companion mass-ratio distribution is a unique probe into the conditions of the collapsing cloud core and circumstellar disk(s) of the binary fragments. Inside a~1000AU the disks from the two forming stars can interact, and additionally companions can form directly through disk fragmentation. We should, therefore, expect the mass-ratio distribution of close companions (a<~100AU) to differ from that of wide companions. This prediction is difficult to test using traditional methods, in particular, with intermediate-mass primary stars, for a variety of observational reasons. We present the results of a survey searching for companions to A- and B-type stars using the direct spectral detection method, which is sensitive to late-type companions within ~1'' of the primary and which has no inner working angle. We estimate the temperatures and surface gravity of most of the 341 sample stars and derive their masses and ages. We additionally estimate the temperatures and masses of the 64 companions we find, 23 of which are new detections. We find that the mass-ratio distribution for our sample has a maximum near q~0.3. Our mass-ratio distribution has a very different form than in previous works, where it is usually well-described by a power law, and indicates that close companions to intermediate-mass stars experience significantly different accretion histories or formation mechanisms than wide companions.
