- ID:
- ivo://CDS.VizieR/J/ApJ/597/323
- Title:
- Cool stars at the Galactic Center
- Short Name:
- J/ApJ/597/323
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present {lambda}/{Delta}{lambda}=550-1200 near-infrared H and K spectra for a magnitude-limited sample of 79 asymptotic giant branch and cool supergiant stars in the central ~5pc (diameter) of the Galaxy. We use a set of similar spectra obtained for solar neighborhood stars with known Teff and Mbol that is in the same range as the Galactic center (GC) sample to derive Teff and Mbol for the GC sample. We then construct the H-R diagram for the GC sample. Using an automated maximum likelihood routine, we derive a coarse star formation history of the GC.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/616/A108
- Title:
- Cool stars chromospheric activity catalog
- Short Name:
- J/A+A/616/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chromospheric activity monitoring of a wide range of cool stars can provide valuable information on stellar magnetic activity and its dependence on fundamental stellar parameters such as effective temperature and rotation. We compile a chromospheric activity catalogue of 4454 cool stars from a combination of archival HARPS spectra and multiple other surveys, including the Mount Wilson data that have recently been released by the NSO. We explore the variation in chromospheric activity of cool stars along the main sequence for stars with different effective temperatures. Additionally, we also perform an activity-cycle period search and investigate its relation with rotation. The chromospheric activity index, S-index, was measured for 304 main-sequence stars from archived high-resolution HARPS spectra. Additionally, the measured and archived S-indices were converted into the chromospheric flux ratio logR'HK. The activity-cycle periods were determined using the generalised Lomb-Scargle periodogram to study the active and inactive branches on the rotation-activity-cycle period plane. The global sample shows that the bimodality of chromospheric activity, known as the Vaughan-Preston gap, is not prominent, with a significant percentage of the stars at an intermediate-activity level around logR'HK=-4.75. Independently, the cycle period search shows that stars can lie in the region intermediate between the active and inactive branch, which means that the active branch is not as clearly distinct as previously thought. The weakening of the Vaughan-Preston gap indicates that cool stars spin down from a higher activity level and settle at a lower activity level without a sudden break at intermediate activity. Some cycle periods are close to the solar value between the active and inactive branch, which suggests that the solar dynamo is most likely a common case of the stellar dynamo.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/1592
- Title:
- Cool stars in galactic clusters
- Short Name:
- J/MNRAS/403/1592
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have investigated the relevant trend of the bolometric correction (BC) at the cool-temperature regime of red giant stars and its possible dependence on stellar metallicity. Our analysis relies on a wide sample of optical-infrared spectroscopic observations, along the 3500{AA}=>2.5um wavelength range, for a grid of 92 red giant stars in five (three globular + two open) Galactic clusters, along the full metallicity range covered by the bulk of the stars, -2.2<=[Fe/H]<=+0.4.
- ID:
- ivo://CDS.VizieR/J/MNRAS/455/4231
- Title:
- Coralie radial velocities for l Car
- Short Name:
- J/MNRAS/455/4231
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Baade-Wesselink-type (BW) techniques enable geometric distance measurements of Cepheid variable stars in the Galaxy and the Magellanic clouds. The leading uncertainties involved concern projection factors required to translate observed radial velocities (RVs) to pulsational velocities and recently discovered modulated variability. We carried out an unprecedented observational campaign involving long-baseline interferometry (VLTI/PIONIER) and spectroscopy (Euler/Coralie) to search for modulated variability in the long-period (P~35.5d) Cepheid {ell} Carinae. We determine highly precise angular diameters from squared visibilities and investigate possible differences between two consecutive maximal diameters, {Delta}_max_{Theta}. We characterize the modulated variability along the line of sight using 360 high-precision RVs. Here we report tentative evidence for modulated angular variability and confirm cycle-to-cycle differences of {ell} Carinae's RV variability. Two successive maxima yield {Delta}_max_{Theta}=13.1+/-0.7(stat.){mu}as for uniform disc models and 22.5+/-1.4(stat.){mu}as (4 percent of the total angular variation) for limb-darkened models. By comparing new RVs with 2014 RVs, we show modulation to vary in strength. Barring confirmation, our results suggest the optical continuum (traced by interferometry) to be differently affected by modulation than gas motions (traced by spectroscopy). This implies a previously unknown time dependence of projection factors, which can vary by 5 percent between consecutive cycles of expansion and contraction. Additional interferometric data are required to confirm modulated angular diameter variations. By understanding the origin of modulated variability and monitoring its long-term behaviour, we aim to improve the accuracy of BW distances and further the understanding of stellar pulsations.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A66
- Title:
- Correlation of logR'HK with logIH{alpha}
- Short Name:
- J/A+A/566/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The re-emission in the cores of the CaII H & K and H{alpha} lines are well known proxies of stellar activity. However, these activity indices probe different activity phenomena: the first is more sensitive to plage variation, while the other is more sensitive to filaments. In this paper, we study the long-term correlation between logR'_HK_ and logI_H{alpha}_, two indices based on the CaII H & K and H{alpha} lines, respectively, for a sample of 271 FGK stars using measurements obtained over a ~9-year time span. Because stellar activity is one of the main obstacles to the detection of low-mass and long-period planets, understanding this activity index correlation further can give us some hints about the optimal target to focus on ways to correct for these activity effects. We found a great variety of long-term correlations between logR'_HK_ and logI_H{alpha}_. Around 20% of our sample has a strong positive correlation between the indices while about 3% show strong negative correlation. These fractions are compatible with those found for the case of early-M dwarfs. Stars exhibiting a positive correlation have a tendency to be more active when compared to the median of the sample, while stars showing a negative correlation are more present among higher metallicity stars. There is also a tendency for the positively correlated stars to be more present among the coolest stars, a result which is probably due to the activity level effect on the correlation. Activity level and metallicity therefore seem to be playing a role on the correlation between logR'_HK_ and logI_H{alpha}_. Possible explanations based on the influence of filaments for the diversity in the correlations between these indices are discussed in this paper. As a parallel result, we show a way to estimate the effective temperature of FGK dwarfs that exhibit a low activity level by using the H{alpha} index.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/2349
- Title:
- C/O vs Mg/Si of planetary systems
- Short Name:
- J/ApJ/725/2349
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Theoretical studies suggest that C/O and Mg/Si are the most important elemental ratios in determining the mineralogy of terrestrial planets. The C/O ratio controls the distribution of Si among carbide and oxide species, while Mg/Si gives information about the silicate mineralogy. We present a detailed and uniform study of C, O, Mg, and Si abundances for 61 stars with detected planets and 270 stars without detected planets from the homogeneous high-quality unbiased HARPS GTO sample, together with 39 more planet-host stars from other surveys. We determine these important mineralogical ratios and investigate the nature of the possible terrestrial planets that could have formed in those planetary systems. We find mineralogical ratios quite different from those of the Sun, showing that there is a wide variety of planetary systems which are not similar to our solar system. Many planetary host stars present an Mg/Si value lower than 1, so their planets will have a high Si content to form species such as MgSiO_3_. This type of composition can have important implications for planetary processes such as plate tectonics, atmospheric composition, or volcanism.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A128
- Title:
- Cygnus OB2 association NIR light curves
- Short Name:
- J/A+A/640/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a J, H, and K photometric variability survey of the central 0.78 square degrees of the young OB association Cygnus OB2. We used data observed with the Wide-Field CAMera at the United Kingdom Infrared Telescope in 2007 (spanning 217 days) to investigate the light curves of 5083 low mass candidate members in the association and explore the occurrence and main characteristics of their near-infrared variability. We identified 2529 stars (~50% of the sample) with significant variability with time-scales ranging from days to months. We classified the variable stars into the following three groups according to their light curve morphology: periodic variability (1697 stars), occultation variability (124 stars), and other types of variability (726 stars). We verified that the disk-bearing stars in our sample are significantly more variable in the near-infrared than diskless stars, with a steep increase in the disk-fraction among stars with higher variability amplitude. We investigated the trajectories described by variable stars in the color-space and measured slopes for 335 stars describing linear trajectories. Based on the trajectories in the color-space, we inferred that the sample analyzed is composed of a mix of young stars presenting variability due to hot and cold spots, extinction by circumstellar material, and changes in the disk emission in the near-infrared. We contemplated using the use of near- infrared variability to identify disk-bearing stars and verified that 53.4% of the known disk-bearing stars in our sample could have been identified as such based solely on their variability. We present 18 newly identified disk- bearing stars and 14 eclipsing binary candidates among CygOB2 lower-mass members.
- ID:
- ivo://CDS.VizieR/J/A+A/582/A68
- Title:
- Database of circumstellar OH masers
- Short Name:
- J/A+A/582/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new database of circumstellar OH masers at 1612, 1665, and 1667MHz in the Milky Way galaxy. The database (version 2.4) contains 13655 observations and 2341 different stars detected in at least one transition. Detections at 1612MHz are considered to be complete until the end of 2014 as long as they were published in refereed papers. Detections of the main lines (1665 and 1667MHz) and non-detections in all transitions are included only if published after 1983. The database contains flux densities and velocities of the two strongest maser peaks, the expansion velocity of the shell, and the radial velocity of the star. Links are provided for about 100 stars (<5% of all stars with OH masers) to interferometric observations and monitoring programs of the maser emission published since their beginnings in the 1970s. Access to the database is possible over the Web (www.hs.uni-hamburg.de/maserdb), allowing cone searches for individual sources and lists of sources. A general search is possible in selected regions of the sky and by defining ranges of flux densities and/or velocities. Alternative ways to access the data are via the German Virtual Observatory and the CDS.
- ID:
- ivo://CDS.VizieR/J/MNRAS/417/1210
- Title:
- DA-white dwarfs from SDSS and UKIDSS
- Short Name:
- J/MNRAS/417/1210
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a method which uses colour-colour cuts on the Sloan Digital Sky Survey (SDSS) photometry to select white dwarfs with hydrogen-rich (DA) atmospheres without the recourse to spectroscopy. This method results in a sample of DA white dwarfs that is 95 per cent complete at an efficiency of returning a true DA white dwarf of 62 per cent. The approach was applied to SDSS Data Release 7 for objects with and without SDSS spectroscopy.
- ID:
- ivo://CDS.VizieR/II/68
- Title:
- Dearborn Catalogue of faint red stars
- Short Name:
- II/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Dearborn Survey is the result of a survey of faint red stars conducted at the Dearborn Observatory from about 1932 to 1947. It covers the declination range -4.5deg to +90deg (54% of the Sky), and consisted of over 1800 direct plates and spectrograms carrying single or multiple exposures varying from a second to 4 hours. The magnitudes in the catalog were obtained from direct plates mostly sensitive in the 0.55-0.64{mu}m wavelength region. The spectral types were obtained from objective-prism plates with red-sensitive emulsion, and were classified on the visibility of the TiO bands.
