- ID:
- ivo://CDS.VizieR/J/A+A/556/A52
- Title:
- {gamma} Dor stars from Kepler
- Short Name:
- J/A+A/556/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The launches of the MOST, CoRoT, and Kepler missions opened up a new era in asteroseismology, the study of stellar interiors via interpretation of pulsation patterns observed at the surfaces of large groups of stars. These space missions deliver a huge amount of high-quality photometric data suitable to study numerous pulsating stars. Our ultimate goal is a detection and analysis of an extended sample of {gamma} Dor-type pulsating stars with the aim to search for observational evidence of non-uniform period spacings and rotational splittings of gravity modes in main-sequence stars typically twice as massive as the Sun. This kind of diagnostic can be used to deduce the internal rotation law and to estimate the amount of rotational mixing in the near core regions. We applied an automated supervised photometric classification method to select a sample of 69 Gamma Doradus ({gamma} Dor) candidate stars. We used an advanced method to extract the Kepler light curves from the pixel data information using custom masks. For 36 of the stars, we obtained high-resolution spectroscopy with the HERMES spectrograph installed at the Mercator telescope. The spectroscopic data are analysed to determine the fundamental parameters like Teff, log g, vsini, and [M/H]. We find that all stars for which spectroscopic estimates of Teff and log g are available fall into the region of the HR diagram, where the {gamma} Dor and {delta} Sct instability strips overlap. The stars cluster in a 700 K window in effective temperature; log g measurements suggest luminosity class IV-V, i.e. sub-giant or main-sequence stars. From the Kepler photometry, we identify 45 {gamma} Dor-type pulsators, 14 {gamma} Dor/{delta} Sct hybrids, and 10 stars, which are classified as "possibly {gamma} Dor/{delta} Sct hybrid pulsators". We find a clear correlation between the spectroscopically derived vsini and the frequencies of independent pulsation modes.
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Search Results
- ID:
- ivo://CDS.VizieR/V/117A
- Title:
- Geneva-Copenhagen Survey of Solar neighbourhood
- Short Name:
- V/117A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (from paper II, 2007) Ages, metallicities, space velocities, and Galactic orbits of stars in the Solar neighbourhood are fundamental observational constraints on models of galactic disk evolution. Understanding and minimising systematic errors and sample selection biases in the data is crucial for their interpretation. We aim to consolidate the calibrations of uvbyb photometry into T_eff_, [Fe/H], distance, and age for F and G stars and rediscuss the results of the Geneva-Copenhagen Survey (GCS, Nordstrom et al., 2004, paper I) in terms of the evolution of the disk. We use recent V-K photometry, angular diameters, high-resolution spectroscopy, Hipparcos parallaxes, and extensive numerical simulations to re-examine and verify the temperature, metallicity, distance, and reddening calibrations for the uvbyb system. We also highlight the selection effects inherent in the apparent-magnitude limited GCS sample. We substantially improve the T_eff_ and [Fe/H] calibrations for early F stars, where spectroscopic temperatures have large systematic errors. A slight offset of the GCS photometry and the non-standard helium abundance of the Hyades invalidate its use for checking metallicity or age scales; however, the distances, reddenings, metallicities, and age scale for GCS field stars require minor corrections only. Our recomputed ages are in excellent agreement with the independent determinations by Takeda et al. (2007ApJS..168..297T), indicating that isochrone ages can now be reliably determined. The revised G-dwarf metallicity distribution remains incompatible with closed-box models, and the age-metallicity relation for the thin disk remains almost flat, with large and real scatter at all ages sigma_intrinsic=0.20 dex). Dynamical heating of the thin disk continues throughout its life; specific in-plane dynamical effects dominate the evolution of the U and V velocities, while the W velocities remain random at all ages. When assigning thick and thin-disk membership for stars from kinematic criteria, parameters for the oldest stars should be used to characterise the thin disk.
- ID:
- ivo://CDS.VizieR/V/130
- Title:
- Geneva-Copenhagen Survey of Solar neighbourhood III
- Short Name:
- V/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ages, chemical compositions, velocity vectors, and Galactic orbits for stars in the solar neighbourhood are fundamental test data for models of Galactic evolution. The Geneva-Copenhagen Survey of the Solar neighbourhood (Nordstrom et al. 2004A&A...418..989N; GCS), a magnitude-complete, kinematically unbiased sample of 16,682 nearby F and G dwarfs, is the largest available sample with complete data for stars with ages spanning that of the disk. We aim to improve the accuracy of the GCS data by implementing the recent revision of the Hipparcos parallaxes. The new parallaxes yield improved astrometric distances for 12,506 stars in the GCS. We also use the parallaxes to verify the distance calibration for uvbyHbeta photometry by Holmberg et al. (2007A&A...475..519H; GCS II, Cat. VI/117). We add new selection criteria to exclude evolved cool stars giving unreliable results and derive distances for 3,580 stars with large parallax errors or not observed by Hipparcos. We also check the GCS II scales of T_eff_ and [Fe/H] and find no need for change. From the new distances we compute revised Mv, U, V, W, and Galactic orbital parameters for 13,520 GCS stars. We also recompute stellar ages with the new values of Mv from the Padova stellar evolution models used in GCS I-II, and compare them with ages from the Yale-Yonsei and Victoria-Regina models. Finally, we compare the observed age-velocity relation in W with three simulated disk heating scenarios to show the potential of the data. With these revisions, the basic data for the GCS stars should now be as reliable as is possible with existing techniques. Further improvement must await consolidation of the T_eff_ scale from angular diameters and fluxes, and the Gaia trigonometric parallaxes. We discuss the conditions for improving computed stellar ages from new input data, and for distinguishing different disk heating scenarios from data sets of the size and precision of the GCS.
- ID:
- ivo://CDS.VizieR/J/A+A/506/85
- Title:
- HD 50844 observed by CoRoT
- Short Name:
- J/A+A/506/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work presents the results obtained on HD 50844, the only delta Sct star observed in the CoRoT Initial Run (57.6d). The aim of these CoRoT observations was to investigate and characterize for the first time the pulsational behaviour of a delta Sct star, when observed at a level of precision and with a much better duty cycle than from the ground. The 140016 datapoints were analysed using independent approaches (SigSpec software and different iterative sine-wave fittings) and several checks performed (splitting of the timeseries in different subsets, investigation of the residual light curves and spectra. A level of 10^-5^mag was reached in the amplitude spectra of the CoRoT timeseries. The space monitoring was complemented by ground-based high-resolution spectroscopy, which allowed the mode identification of 30 terms. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0-30d^-1^. All the cross-checks confirmed this new result. The initial guess that delta Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high-degree modes (up to ell=14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground-based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. Probably due to this unfavourable evolutionary status, no clear regular distribution is observed in the frequency set. The predominant term f1=6.92d^-1^ has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data. The CoRoT scientific programme contains other delta Sct stars, with different evolutionary statuses. The very rich and dense frequency spectrum discovered in the light curve of HD 50844 is the starting point for future investigations.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A65
- Title:
- HD113337 radial velocity
- Short Name:
- J/A+A/561/A65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the frame of the search for extrasolar planets and brown dwarfs around early-type main-sequence stars, we present the detection of a giant planet around the young F-type star HD113337. We estimated the age of the system to be 150^+100^_-50_Myr. Interestingly, an IR excess attributed to a cold debris disk was previously detected on this star. The SOPHIE spectrograph on the 1.93m telescope at the Observatoire de Haute-Provence (OHP) was used to obtain ~300 spectra over 6 years. We used our SAFIR tool, dedicated to the spectra analysis of A and F stars, to derive the radial velocity variations. The data reveal a 324.0^+1.7^_-3.3_days period that we attribute to a giant planet with a minimum mass of 2.83+/-0.24MJup in an eccentric orbit with e=0.46+/-0.04. A long-term quadratic drift, that we assign to be probably of stellar origin, is superimposed to the Keplerian solution.
- ID:
- ivo://CDS.VizieR/J/ApJ/746/154
- Title:
- Improved kinematic parallaxes for Sco-Cen members
- Short Name:
- J/ApJ/746/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the ages and star formation history of the F-type stars in the Upper Scorpius (US), Upper Centaurus-Lupus (UCL), and Lower Centaurus-Crux (LCC) subgroups of Scorpius-Centaurus (Sco-Cen), the nearest OB association. Our parent sample is the kinematically selected Hipparcos sample of de Zeeuw et al. (1999, Cat. J/AJ/117/354), restricted to the 138 F-type members. We have obtained classification-resolution optical spectra and have also determined the spectroscopic accretion disk fraction. With Hipparcos and 2MASS photometry, we estimate the reddening and extinction for each star and place the candidate members on a theoretical H-R diagram. For each subgroup we construct empirical isochrones and compare to published evolutionary tracks.
- ID:
- ivo://CDS.VizieR/J/AJ/119/1448
- Title:
- Improved properties for cool stars
- Short Name:
- J/AJ/119/1448
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new grids of colors and bolometric corrections for F-K stars having 4000 K {<=} Teff {<=} 6500 K, 0.0 {<=} log(g) {<=} 4.5, and -3.0 {<=} [Fe/H] {<=} 0.0. Colors are tabulated for Johnson U-V and B-V, Cousins V-R and V-I, Johnson-Glass V-K, J-K, and H-K, and CIT/CTIO V-K, J-K, H-K, and CO. We have developed these color-temperature relations by convolving synthetic spectra with the best-determined, photometric filter transmission profiles. The synthetic spectra have been computed with the SSG spectral synthesis code (Bell & Gustafsson 1978; Gustafsson & Bell 1979) using MARCS stellar atmosphere models (Gustafsson et al. 1975; Bell et al. 1976) as input. Both of these codes have been improved substantially, especially at low temperatures, through the incorporation of new opacity data. The resulting synthetic colors have been put onto the observational systems by applying color calibrations derived from models and photometry of field stars that have effective temperatures determined by the infrared flux method. These color calibrations have zero points that change most of the original synthetic colors by less than 0.02 mag, and the corresponding slopes generally alter the colors by less than 5%.
- ID:
- ivo://CDS.VizieR/J/ApJ/853/77
- Title:
- KIC 8462852 ASAS V-band long-term variability
- Short Name:
- J/ApJ/853/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ~800 days of photometric monitoring of Boyajian's Star (KIC8462852) from the All-Sky Automated Survey for Supernovae (ASAS-SN) and ~4000d of monitoring from the All Sky Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian's Star has steadily decreased at a rate of 6.3+/-1.4mmag/yr, such that the star is now 1.5% fainter than it was in 2015 February. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian's Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a monotonic decline. We analyze a sample of ~1000 comparison stars of similar brightness located in the same ASAS-SN field and demonstrate that the recent fading is significant at >=99.4% confidence. The 2015-2017 dimming rate is consistent with that measured with Kepler data for the time period from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models for the star's behavior proposed to date.
- ID:
- ivo://CDS.VizieR/J/A+A/409/251
- Title:
- Li abundances and velocities in F and G stars
- Short Name:
- J/A+A/409/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lithium abundances have been determined in 127 F and G Pop I stars based on new measurements of the equivalent width of the {lambda}6707{AA} Li I line from their high resolution CCD spectra. Distances and absolute magnitudes of these stars have been obtained from the Hipparcos Catalogue (<I/239>) and their masses and ages derived, enabling us to investigate the behaviour of lithium as a function of these parameters. Based on their location on the HR diagram superposed on theoretical evolutionary tracks, the sample of the stars has been chosen to ensure that they have more or less completed their Li depletion on the main sequence.
- ID:
- ivo://CDS.VizieR/J/A+A/576/A69
- Title:
- Li abundances in F stars
- Short Name:
- J/A+A/576/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim, on the one hand, to study the possible differences of Li abundances between planet hosts and stars without detected planets at effective temperatures hotter than the Sun, and on the other hand, to explore the Li dip and the evolution of Li at high metallicities. We present lithium abundances for 353 main sequence stars with and without planets in the T_eff_ range 5900-7200K. We observed 265 stars of our sample with HARPS spectrograph during different planets search programs. We observed the remaining targets with a variety of high-resolution spectrographs. The abundances are derived by a standard local thermodynamic equilibrium analysis using spectral synthesis with the code MOOG and a grid of Kurucz ATLAS9 atmospheres. We find that hot jupiter host stars within the T_eff_ range 5900-6300K show lower Li abundances, by 0.14dex, than stars without detected planets. This offset has a significance at the level 7{sigma}, pointing to a stronger effect of planet formation on Li abundances when the planets are more massive and migrate close to the star. However, we also find that the average vsini of (a fraction of) stars with hot jupiters is higher on average than for single stars in the same T_eff_ region, suggesting that rotational-induced mixing (and not the presence of planets) might be the cause for a greater depletion of Li. We confirm that the mass-metallicity dependence of the Li dip is extended towards [Fe/H]~0.4dex (beginning at [Fe/H]~-0.4dex for our stars) and that probably reflects the mass-metallicity correlation of stars of the same T_eff_ on the main sequence. We find that for the youngest stars (<1.5Gyr) around the Li dip, the depletion of Li increases with vsini values, as proposed by rotationally-induced depletion models. This suggests that the Li dip consists of fast rotators at young ages whereas the most Li-depleted old stars show lower rotation rates (probably caused by the spin-down during their long lifes). We have also explored the Li evolution with [Fe/H] taking advantage of the metal-rich stars included in our sample. We find that Li abundance reaches its maximum around solar metallicity, but decreases in the most metal-rich stars, as predicted by some models of Li Galactic production.
