- ID:
- ivo://CDS.VizieR/J/ApJS/244/27
- Title:
- Radial velocity measurements in LAMOST-II
- Short Name:
- J/ApJS/244/27
- Date:
- 09 Dec 2021
- Publisher:
- CDS
- Description:
- The radial velocity (RV) is a basic physical quantity that can be determined through the Doppler shift of the spectrum of a star. The precision of the RV measurement depends on the resolution of the spectrum we used and the accuracy of wavelength calibration. In this work, radial velocities of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope-II (LAMOST-II) medium-resolution (R~7500) spectra are measured for 1,594,956 spectra (each spectrum has two wavebands) through matching with templates. A set of RV standard stars are used to recalibrate the zero point of the measurement, and some reference sets with RVs derived from medium-/high-resolution observations are used to evaluate the accuracy of the measurement. By comparing with reference sets, the accuracy of our measurement can get 0.0277km/s with respect to radial velocities of standard stars. The intrinsic precision is estimated with the multiple observations of single stars, which can be achieved to 1.36km/s, 1.08km/s, and 0.91km/s for the spectra at signal-to-noise levels of 10, 20, and 50, respectively.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/860/1
- Title:
- Radial velocity measurements of 20 EBs in LMC
- Short Name:
- J/ApJ/860/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a determination of the precise fundamental physical parameters of 20 detached, double-lined, eclipsing binary stars in the Large Magellanic Cloud (LMC) containing G- or early K-type giant stars. Eleven are new systems; the remaining nine are systems already analyzed by our team for which we present updated parameters. The catalog results from our long-term survey of eclipsing binaries in the Magellanic Clouds suitable for high-precision determination of distances (the Araucaria Project). The V-band brightnesses of the systems range from 15.4 to 17.7mag, and their orbital periods range from 49 to 773days. Six systems have favorable geometry showing total eclipses. The absolute dimensions of all eclipsing binary components are calculated with a precision of better than 3%, and all systems are suitable for a precise distance determination. The measured stellar masses are in the range 1.4 to 4.6M_{sun}_, and comparison with the MESA isochrones gives ages between 0.1 and 2.1Gyr. The systems show an age-metallicity relation with no evolution of metallicity for systems older than 0.6Gyr, followed by a rise to a metallicity maximum at age 0.5Gyr and then a slow metallicity decrease until 0.1Gyr. Two systems have components with very different masses: OGLE LMC-ECL-05430 and OGLE LMC-ECL-18365. Neither system can be fitted by a single stellar evolution isochrone, explained by a past mass transfer scenario in the case of ECL-18365 and a gravitational capture or hierarchical binary merger scenario in the case of ECL-05430. The longest-period system, OGLE LMC SC9_230659, shows a surprising apsidal motion that shifts the apparent position of the eclipses. This is a clear sign of a physical companion to the system; however, neither investigation of the spectra nor light-curve analysis indicates a third-light contribution larger than 2%-3%. In one spectrum of OGLE LMC-ECL-12669, we noted a peculiar dimming of one of the components by 65% well outside of the eclipses. We interpret this observation as arising from an extremely rare occultation event, as a foreground Galactic object covers only one component of an extragalactic eclipsing binary.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/34
- Title:
- Radial velocity monitoring of 5 FGK stars
- Short Name:
- J/ApJ/818/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of two new long-period giant planets orbiting the stars HD 95872 and HD 162004 ({psi}^1^ Dra B) by the McDonald Observatory planet search. The planet HD 95872b has a minimum mass of 4.6M_Jup_ and an orbital semimajor axis of 5.2AU. The giant planet {psi}^1^ Dra Bb has a minimum mass of 1.5M_Jup_ and an orbital semimajor axis of 4.4AU. Both of these planets qualify as Jupiter analogs. These results are based on over one and a half decades of precise radial velocity (RV) measurements collected by our program using the McDonald Observatory Tull Coude spectrograph at the 2.7m Harlan J. Smith Telescope. In the case of {psi}^1^ Dra B we also detect a long-term nonlinear trend in our data that indicates the presence of an additional giant planet, similar to the Jupiter-Saturn pair. The primary of the binary star system, {psi}^1^ Dra A, exhibits a very large amplitude RV variation due to another stellar companion. We detect this additional member using speckle imaging. We also report two cases --HD 10086 and HD 102870 ({beta} Virginis)-- of significant RV variation consistent with the presence of a planet, but that are probably caused by stellar activity, rather than reflexive Keplerian motion. These two cases stress the importance of monitoring the magnetic activity level of a target star, as long-term activity cycles can mimic the presence of a Jupiter-analog planet.
- ID:
- ivo://CDS.VizieR/J/AJ/157/52
- Title:
- Radial velocity observations in super-Earth systems
- Short Name:
- J/AJ/157/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use radial velocity (RV) observations to search for long-period gas giant companions in systems hosting inner super-Earth (1-4 R_{Earth}_, 1-10 M_{Earth}_) planets to constrain formation and migration scenarios for this population. We consistently refit published RV data sets for 65 stars and find nine systems with statistically significant trends indicating the presence of an outer companion. We combine these RV data with AO images to constrain the masses and semi-major axes of these companions. We quantify our sensitivity to the presence of long-period companions by fitting the sample with a power-law distribution and find an occurrence rate of 39%+/-7% for companions 0.5-20 M_Jup_ and 1-20 au. Half of our systems were discovered by the transit method, and half were discovered by the RV method. While differences in the RV baselines and number of data points between the two samples lead to different sensitivities to distant companions, we find that occurrence rates of gas giant companions in each sample are consistent at the 0.5{sigma} level. We compare the frequency of Jupiter analogs in these systems to the equivalent rate from field star surveys and find that Jupiter analogs are more common around stars hosting super-Earths. We conclude that the presence of outer gas giants does not suppress the formation of inner super-Earths, and that these two populations of planets instead appear to be correlated. We also find that the stellar metallicities of systems with gas giant companions are higher than those without companions, in agreement with the well-established metallicity correlation from RV surveys of field stars.
- ID:
- ivo://CDS.VizieR/J/A+A/625/A68
- Title:
- Radii and masses of the CARMENES targets
- Short Name:
- J/A+A/625/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine the radii and masses of 293 nearby, bright M dwarfs of the CARMENES survey. This is the first time that such a large and homogeneous high-resolution (R>80000) spectroscopic survey has been used to derive these fundamental stellar parameters. We derived the radii using Stefan-Boltzmann's law. We obtained the required effective temperatures Teff from a spectral analysis and we obtained the required luminosities L from integrated broadband photometry together with the Gaia DR2 parallaxes. The mass was then determined using a mass-radius relation that we derived from eclipsing binaries known in the literature. We compared this method with three other methods: (1) We calculated the mass from the radius and the surface gravity logg, which was obtained from the same spectral analysis as Teff. (2) We used a widely used infrared mass-magnitude relation. (3) We used a Bayesian approach to infer stellar parameters from the comparison of the absolute magnitudes and colors of our targets with evolutionary models. Between spectral types M0V and M7V our radii cover the range 0.1R_{sun}_<R<0.6R_{sun}_ with an error of 2-3% and our masses cover 0.09M_{sun}_<M<0.6M_{sun}_ with an error of 3-5%. We find good agreement between the masses determined with these different methods for most of our targets. Only the masses of very young objects show discrepancies. This can be well explained with the assumptions that we used for our methods.
- ID:
- ivo://CDS.VizieR/J/AJ/157/63
- Title:
- Radius relations for low-metallicity M-dwarf stars
- Short Name:
- J/AJ/157/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- M subdwarfs are low-metallicity M dwarfs that typically inhabit the halo population of the Galaxy. Metallicity controls the opacity of stellar atmospheres; in metal-poor stars, hydrostatic equilibrium is reached at a smaller radius, leading to smaller radii for a given effective temperature. We compile a sample of 88 stars that span spectral classes K7 to M6 and include stars with metallicity classes from solar-metallicity dwarf stars to the lowest metallicity ultra subdwarfs to test how metallicity changes the stellar radius. We fit models to Palomar Double Spectrograph (DBSP) optical spectra to derive effective temperatures (T_eff_) and we measure bolometric luminosities (L_bol_) by combining broad wavelength-coverage photometry with Gaia parallaxes. Radii are then computed by combining the T_eff_ and L_bol_ using the Stefan-Boltzman law. We find that for a given temperature, ultra subdwarfs can be as much as five times smaller than their solar-metallicity counterparts. We present color-radius and color-surface brightness relations that extend down to [Fe/H] of -2.0 dex, in order to aid the radius determination of M subdwarfs, which will be especially important for the WFIRST exoplanetary microlensing survey.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A106
- Title:
- RAVE open cluster pairs, groups and complexes
- Short Name:
- J/A+A/600/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic open clusters (OCs) mainly belong to the young stellar population in the Milky Way disk, but are there groups and complexes of OCs that possibly define an additional level in hierarchical star formation? Current compilations are too incomplete to address this question, especially regarding radial velocities (RVs) and metallicities ([M/H]). Here we present the parameters for the final working sample of 432 open clusters, as well as the mean parameters for the 19 detected potential open cluster groupings.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/L7
- Title:
- Red clump stars selected from LAMOST and APOGEE
- Short Name:
- J/ApJ/858/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Core helium-burning red clump (RC) stars are excellent standard candles in the Milky Way. These stars may have more precise distance estimates from spectrophotometry than from Gaia parallaxes beyond 3kpc. However, RC stars have values of Teff and logg that are very similar to some red giant branch (RGB) stars. Especially for low-resolution spectroscopic studies where Teff, logg, and [Fe/H] can only be estimated with limited precision, separating RC stars from RGB through established methods can incur ~20% contamination. Recently, Hawkins+ (2018ApJ...853...20H) demonstrated that the additional information in single-epoch spectra, such as the C/N ratio, can be exploited to cleanly differentiate RC and RGB stars. In this second paper of the series, we establish a data-driven mapping from spectral flux space to independently determined asteroseismic parameters, the frequency and the period spacing. From this, we identify 210371 RC stars from the publicly available LAMOST DR3 and APOGEE DR14 data, with ~9% of contamination. We provide an RC sample of 92249 stars with a contamination of only ~3%, by restricting the combined analysis to LAMOST stars with S/N_pix_>=75. This demonstrates that high-signal-to-noise ratio (S/N), low-resolution spectra covering a broad wavelength range can identify RC samples at least as pristine as their high- resolution counterparts. As coming and ongoing surveys such as TESS, DESI, and LAMOST will continue to improve the overlapping training spectroscopic-asteroseismic sample, the method presented in this study provides an efficient and straightforward way to derive a vast yet pristine sample of RC stars to reveal the three-dimensional (3D) structure of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/870/115
- Title:
- Reddening, distance modulus & Fe/H of RRLs in w Cen
- Short Name:
- J/ApJ/870/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We developed a new approach to provide accurate estimates of the metal content, reddening, and true distance modulus of RR Lyrae stars (RRLs). The method is based on homogeneous optical (BVI) and near-infrared (JHK) mean magnitudes and on predicted period-luminosity-metallicity relations (IJHK) and absolute mean magnitude-metallicity relations (BV). We obtained solutions for three different RRL samples in {omega}Cen: first overtone (RRc, 90), fundamental (RRab, 80), and global (RRc+RRab) in which the period of first overtones were fundamentalized. The metallicity distribution shows a well defined peak at [Fe/H]~-1.98 and a standard deviation of {sigma}=0.54dex. The spread is, as expected, metal-poor ([Fe/H]<=-2.3) objects. The current metallicity distribution is ~0.3dex more metal-poor than similar estimates for RRLs available in the literature. The difference vanishes if the true distance modulus we estimated is offset by -0.06/-0.07mag in true distance modulus. We also found a cluster true distance modulus of {mu}=13.720{+/-}0.002{+/-}0.030mag, where the former error is the error on the mean and the latter is the standard deviation. Moreover, we found a cluster reddening of E(B-V)=0.132{+/-}0.002{+/-}0.028mag and spatial variations of the order of a few arcmin across the body of the cluster. Both the true distance modulus and the reddening are slightly larger than similar estimates available in the literature, but the difference is within 1{sigma}. The metallicity dependence of distance diagnostics agrees with theory and observations, but firm constraints require accurate and homogeneous spectroscopic measurements.
- ID:
- ivo://CDS.VizieR/J/ApJ/810/148
- Title:
- Red giant abundances in NGC 2808
- Short Name:
- J/ApJ/810/148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical composition of multiple populations in the massive globular cluster (GC) NGC 2808 is addressed with the homogeneous abundance reanalysis of 140 red giant branch stars. UVES spectra for 31 stars and GIRAFFE spectra for the other giants were analyzed with the same procedures used for about 2500 giants in 23 GCs in our FLAMES survey, deriving abundances of Fe, O, Na, Mg, Si, Ca, Ti, Sc, Cr, Mn, and Ni. Iron, elements from {alpha} capture, and those in the Fe group do not show intrinsic scatter. On our UVES scale, the metallicity of NGC 2808 is [Fe/H]=-1.29+/-0.005+/-0.034 (+/-statistical+/-systematic error) with {sigma}=0.030 (31 stars). The main features related to proton-capture elements are retrieved, but the improved statistics and the smaller associated internal errors allow us to uncover five distinct groups of stars along the Na-O anticorrelation. We observe large depletions in Mg, anticorrelated with enhancements of Na and also Si, suggestive of unusually high temperatures for proton captures. About 14% of our sample is formed by giants with solar or subsolar [Mg/Fe] ratios. Using the [Na/Mg] ratios, we confirm the presence of five populations with different chemical compositions that we call P1, P2, I1, I2, and E in order of decreasing Mg and increasing Na abundances. Statistical tests show that the mean ratios in any pair of groups cannot be extracted from the same parent distribution. The overlap with the five populations recently detected from UV photometry is good but not perfect, confirming that more distinct components probably exist in this complex GC.
