- ID:
- ivo://CDS.VizieR/J/AJ/155/177
- Title:
- Obliquities of planetary & eclipsing binary systems
- Short Name:
- J/AJ/155/177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The light curve of an eclipsing system shows anomalies whenever the eclipsing body passes in front of active regions on the eclipsed star. In some cases, the pattern of anomalies can be used to determine the obliquity {Psi} of the eclipsed star. Here we present a method for detecting and analyzing these patterns, based on a statistical test for correlations between the anomalies observed in a sequence of eclipses. Compared to previous methods, ours makes fewer assumptions and is easier to automate. We apply it to a sample of 64 stars with transiting planets and 24 eclipsing binaries for which precise space-based data are available, and for which there was either some indication of flux anomalies or a previously reported obliquity measurement. We were able to determine obliquities for 10 stars with hot Jupiters. In particular we found {Psi}~<10{deg} for Kepler-45, which is only the second M dwarf with a measured obliquity. The other eight cases are G and K stars with low obliquities. Among the eclipsing binaries, we were able to determine obliquities in eight cases, all of which are consistent with zero. Our results also reveal some common patterns of stellar activity for magnetically active G and K stars, including persistently active longitudes.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AN/331/349
- Title:
- O, B-type & red supergiant masses and luminosities
- Short Name:
- J/AN/331/349
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive stars are of interest as progenitors of supernovae, i.e. neutron stars and black holes, which can be sources of gravitational waves. Recent population synthesis models can predict neutron star and gravitational wave observations but deal with a fixed supernova rate or an assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernova progenitors, i.e. with O- and early B-type stars, and also all supergiants within 3kpc. We restrict our sample to those massive stars detected both in 2MASS and observed by Hipparcos, i.e. only those stars with parallax and precise photometry. To determine the luminosities we calculated the extinctions from published multi-colour photometry, spectral types, luminosity class, all corrected for multiplicity and recently revised Hipparcos distances. We use luminosities and temperatures to estimate the masses and ages of these stars using different models from different authors.
- ID:
- ivo://CDS.VizieR/J/ApJ/748/14
- Title:
- ONC population data from WFI observations
- Short Name:
- J/ApJ/748/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new census of the Orion Nebula Cluster over a large field of view (>~30'x30'), significantly increasing the known population of stellar and substellar cluster members with precisely determined properties. We develop and exploit a technique to determine stellar effective temperatures from optical colors, nearly doubling the previously available number of objects with effective temperature determinations in this benchmark cluster. Our technique utilizes colors from deep photometry in the I band and in two medium-band filters at {lambda}~753 and 770nm, which accurately measure the depth of a molecular feature present in the spectra of cool stars. From these colors we can derive effective temperatures with a precision corresponding to better than one-half spectral subtype, and importantly this precision is independent of the extinction to the individual stars. Also, because this technique utilizes only photometry redward of 750nm, the results are only mildly sensitive to optical veiling produced by accretion. Completing our census with previously available data, we place some 1750 sources in the Hertzsprung-Russell diagram and assign masses and ages down to 0.02M_{sun}_. At faint luminosities, we detect a large population of background sources which is easily separated in our photometry from the bona fide cluster members. The resulting initial mass function of the cluster has good completeness well into the substellar mass range, and we find that it declines steeply with decreasing mass. This suggests a deficiency of newly formed brown dwarfs in the cluster compared to the Galactic disk population.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A93
- Title:
- On the metallicity of open clusters. II.
- Short Name:
- J/A+A/561/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The literature was searched for [Fe/H] estimates of individual member stars of open clusters (OCs) based on the analysis of high-resolution spectra. The lower limit for spectral resolving power (R={lambda}/{Delta}{lambda}) was set to 25000, and the lower limit for signal-to-noise ratio was set to 50. We searched the PASTEL database (2010A&A...515A.111S, Cat. B/pastel) and the recent literature for such metallicity determinations in references posterior to 1990 and until June 2013. Only stars with an effective temperature lower than 7000K were included to avoid rapid rotators and chemical peculiarities. We eliminated confirmed non-members, spectroscopic binaries, and chemically peculiar stars and kept only stars with a high probability of membership. This resulted in a list of 571 stars in 86 OCs, with 830 metallicity determinations from 94 papers, which we call the starting sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/723/1542
- Title:
- Optical high-resolution spectroscopy of WTTSs
- Short Name:
- J/ApJ/723/1542
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution spectroscopic observations for a sample of 19 weak-line T Tauri stars (WTTSs). Based on these observations and data of 108 WTTSs taken from the literature, we derive lithium abundances for 127 WTTSs. Investigation of a possible relation between lithium and rotation in WTTSs shows that: (1) rapidly rotating WTTSs have comparatively lower lithium abundances than their slower rotating counterparts; (2) in the spectral-type range G0-K0, most of the WTTSs share the same Li content irrespective of their Teff; and (3) active late-type binaries do not obey the correlation between lithium abundances and rotation periods, since the tidally locked rotation of the late-type binary system leads naturally to slower lithium destruction rates.
- ID:
- ivo://CDS.VizieR/J/ApJ/844/138
- Title:
- Optical spectroscopy toward Orion B fields
- Short Name:
- J/ApJ/844/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from high-resolution optical spectra toward 66 young stars in the Orion B molecular cloud to study their kinematics and other properties. Observations of the H{alpha} and Li I 6707{AA} lines are used to check membership and accretion properties. While the stellar radial velocities of NGC 2068 and L1622 are in good agreement with that of the molecular gas, many of the stars in NGC 2024 show a considerable offset. This could be a signature of either the expansion of the cluster, the high degree of the ejection of the stars from the cluster through dynamical interaction, or the acceleration of the gas due to stellar feedback.
- ID:
- ivo://CDS.VizieR/J/AJ/155/188
- Title:
- Origin of nuclear activity in low-power radio galaxies
- Short Name:
- J/AJ/155/188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using large samples containing nearly 2300 active galaxies of low radio luminosity (1.4 GHz luminosity between 2x10^23^ and 3x10^25^ W/Hz, essentially low-excitation radio galaxies) at z~<0.3, we present a self-contained analysis of the dependence of the nuclear radio activity on both intrinsic and extrinsic properties of galaxies, with the goal of identifying the best predictors of the nuclear radio activity. While confirming the established result that stellar mass must play a key role on the triggering of radio activities, we point out that for the central, most massive galaxies, the radio activity also shows a strong dependence on halo mass, which is not likely due to enhanced interaction rates in denser regions in massive, cluster-scale halos. We thus further investigate the effects of various properties of the intracluster medium (ICM) in massive clusters on the radio activities, employing two standard statistical tools, principle component analysis and logistic regression. It is found that ICM entropy, local cooling time, and pressure are the most effective in predicting the radio activity, pointing to the accretion of gas cooling out of a hot atmosphere to be the likely origin in triggering such activities in galaxies residing in massive dark matter halos. Our analysis framework enables us to logically discern the mechanisms responsible for the radio activity separately for central and satellite galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/595/1154
- Title:
- Oxygen abundances in metal-poor stars
- Short Name:
- J/ApJ/595/1154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present oxygen abundances derived from both the permitted and forbidden oxygen lines for 54 subgiants and giants with [Fe/H] values between -2.7 and solar with the goal of understanding the discrepancy in the derived abundances. A first attempt, using Teff values from photometric calibrations and surface gravities from luminosities obtained agreement between the indicators for turn-off stars, but the disagreement was large for evolved stars. We find that the difference in the oxygen abundances derived from the permitted and forbidden lines is most strongly affected by Teff, and we derive a new Teff scale based on forcing the two sets of lines to give the same oxygen abundances. These new parameters, however, do not agree with other observables, such as theoretical isochrones or Balmer-line profile based Teff determinations. Our analysis finds that one-dimensional, LTE analyses (with published non-LTE corrections for the permitted lines) cannot fully resolve the disagreement in the two indicators without adopting a temperature scale that is incompatible with other temperature indicators. We also find no evidence of circumstellar emission in the forbidden lines, removing such emission as a possible cause for the discrepancy.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/164
- Title:
- Oxygen abundances of dwarf stars
- Short Name:
- J/ApJ/757/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Oxygen abundances of 67 dwarf stars in the metallicity range -1.6<[Fe/H]<-0.4 are derived from a non-LTE analysis of the 777nm OI triplet lines. These stars have precise atmospheric parameters measured by Nissen and Schuster (Cat. J/A+A/511/L10), who find that they separate into three groups based on their kinematics and {alpha}-element (Mg, Si, Ca, Ti) abundances: thick disk, high-{alpha} halo, and low-{alpha} halo. We find the oxygen abundance trends of thick-disk and high-{alpha} halo stars very similar. The low-{alpha} stars show a larger star-to-star scatter in [O/Fe] at a given [Fe/H] and have systematically lower oxygen abundances compared to the other two groups. Thus, we find the behavior of oxygen abundances in these groups of stars similar to that of the {alpha} elements. We use previously published oxygen abundance data of disk and very metal-poor halo stars to present an overall view (-2.3<[Fe/H]<+0.3) of oxygen abundance trends of stars in the solar neighborhood. Two field halo dwarf stars stand out in their O and Na abundances. Both G53-41 and G150-40 have very low oxygen and very high sodium abundances, which are key signatures of the abundance anomalies observed in globular cluster (GC) stars. Therefore, they are likely field halo stars born in GCs. If true, we estimate that at least 3%+/-2% of the local field metal-poor star population was born in GCs.
- ID:
- ivo://CDS.VizieR/J/AJ/152/19
- Title:
- Pan-Pacific Planet Search (PPPS). V. 164 stars
- Short Name:
- J/AJ/152/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectroscopic stellar parameters for the complete target list of 164 evolved stars from the Pan-Pacific Planet Search, a five-year radial velocity campaign using the 3.9m Anglo-Australian Telescope. For 87 of these bright giants, our work represents the first determination of their fundamental parameters. Our results carry typical uncertainties of 100K, 0.15dex, and 0.1dex in T_eff_, logg, and [Fe/H] and are consistent with literature values where available. The derived stellar masses have a mean of 1.31_-0.25_^+0.28^M_{Sun}_, with a tail extending to ~2M_{Sun}_, consistent with the interpretation of these targets as "retired" A-F type stars.
