- ID:
- ivo://CDS.VizieR/J/A+A/574/A124
- Title:
- Spectroscopy of solar twins and analogues
- Short Name:
- J/A+A/574/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many large stellar surveys have been and are still being carried out, providing huge amounts of data, for which stellar physical parameters will be derived. Solar twins and analogues provide a means to test the calibration of these stellar catalogues because the Sun is the best-studied star and provides precise fundamental parameters. Solar twins should be centred on the solar values. This spectroscopic study of solar analogues selected from the Geneva-Copenhagen Survey (GCS) at a resolution of 48000 provides effective temperatures and metallicities for these stars. We test whether our spectroscopic parameters, as well as the previous photometric calibrations, are properly centred on the Sun. In addition, we search for more solar twins in our sample. The methods used in this work are based on literature methods for solar twin searches and on methods we developed in previous work to distinguish the metallicity-temperature degeneracies in the differential comparison of spectra of solar analogues versus a reference solar reflection spectrum.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/143/98
- Title:
- Spectroscopy of star-forming regions in NGC 4194
- Short Name:
- J/AJ/143/98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of long-slit spectroscopy at position angles 68{deg}, 131{deg}, and 164{deg} for the minor-merger NGC 4194, a luminous infrared starburst galaxy. The mass within 1.2kpc of the dynamical center is estimated to be 4.8*109 to 1.7*1010 M{sun}, depending on the assumed inclination to the plane of the sky. The star formation rate (SFR) in the areas sampled is 8 M{sun}/yr. The metallicity, log(O/H)+12, ranges from ~8.8 to >9.0 in regions of significant star formation, suggesting that the metallicity has been enhanced by the current star formation. The star-forming regions range in age from 5 to 9Myr, with the youngest ages occurring in the regions of high SFR. Electron temperatures and the location of the spectra in emission line diagnostic diagrams suggest the presence of shock waves, presumably due to the presence of supernovae, winds from massive stars, and/or collisions of clouds due to the merger. The presence of massive stars and supernovae is consistent with the ages determined for the star-forming regions. The ages of the continua produced by the stellar population are estimated to range from 10Myr to 5Gyr. Much of the stellar population represented in the continua was probably formed before the merger and represents the progenitor galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/705/1481
- Title:
- Spectroscopy of stars in 6 globular clusters
- Short Name:
- J/ApJ/705/1481
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Intermediate resolution spectra at the CaII triplet have been obtained for 55 candidate red giants in the field of the globular cluster M22 with the VLT/FORS2 instrument. Spectra were also obtained for a number of red giants in standard globular clusters to provide a calibration of the observed line strengths with overall abundance [Fe/H]. For the 41 M22 member stars that lie within the V-V_HB_ bounds of the calibration, we find an abundance distribution that is substantially broader than that expected from the observed errors alone. We argue that this broad distribution cannot be the result of differential reddening. Instead, we conclude that, as has long been suspected, M22 is similar to {omega} Cen in having an intrinsic dispersion in heavy element abundance. The observed M22 abundance distribution rises sharply to a peak at [Fe/H]~-1.9 with a broad tail to higher abundances: the highest abundance star in our sample has [Fe/H] ~-1.45dex. If the unusual properties of {omega} Cen have their origin in a scenario in which the cluster is the remnant nucleus of a disrupted dwarf galaxy, then such a scenario likely also applies to M22.
- ID:
- ivo://CDS.VizieR/J/AJ/149/204
- Title:
- Spectroscopy of 25 stars in M68
- Short Name:
- J/AJ/149/204
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present a detailed high-resolution spectroscopic study of post main sequence stars in the globular cluster (GC) M68. Our sample, which covers a range of 4000K in T_eff_, and 3.5dex in log(g), is comprised of members from the red giant, red horizontal, and blue horizontal branch, making this the first high-resolution GC study covering such a large evolutionary and parameter space. Initially, atmospheric parameters were determined using photometric as well as spectroscopic methods, both of which resulted in unphysical and unexpected T_eff_, log(g), {xi}_t_, and [Fe/H] combinations. We therefore developed a hybrid approach that addresses most of these problems, and yields atmospheric parameters that agree well with other measurements in the literature. Furthermore, our derived stellar metallicities are consistent across all evolutionary stages, with <[Fe/H]>=-2.42 ({sigma}=0.14) from 25 stars. Chemical abundances obtained using our methodology also agree with previous studies and bear all the hallmarks of GCs, such as a Na-O anti-correlation, constant Ca abundances, and mild r-process enrichment.
1595. Spectroscopy of Terzan 5
- ID:
- ivo://CDS.VizieR/J/ApJ/726/L20
- Title:
- Spectroscopy of Terzan 5
- Short Name:
- J/ApJ/726/L20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the chemical abundance analysis of 33 red giant stars belonging to the complex stellar system Terzan 5. We confirm the discovery of two stellar populations with distinct iron abundances: a relatively metal-poor component with [Fe/H]=-0.25+/-0.07rms and another component with [Fe/H]=+0.27+/-0.04rms, exceeding in metallicity any known Galactic globular cluster (GC). The two populations also show different [{alpha}/Fe] abundance ratios. The metal-poor component has an average [{alpha}/Fe]=+0.34+/-0.06rms, consistent with the canonical scenario for rapid enrichment by core collapse supernovae (SNe). The metal-rich component has [{alpha}/Fe]=+0.03+/-0.04rms, suggesting that the gas from which it formed was polluted by both type II and type Ia SNe on a longer timescale. Neither of the two populations shows evidence of the [Al/Fe] over [O/Fe] anti-correlation that is typically observed in Galactic GCs. Because these chemical abundance patterns are unique, we propose that Terzan 5 is not a true GC, but a stellar system with a much more complex history of star formation and chemical enrichment.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A107
- Title:
- Spectroscopy of the Eri 2 cluster
- Short Name:
- J/A+A/635/A107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been shown that the ultra-faint dwarf galaxy Eridanus 2 may host a stellar cluster in its centre. If this cluster is shown to exist, it can be used to set constraints on the mass and abundance of massive astrophysical compact halo objects (MACHOs) as a form of dark matter. Previous research has shown promising expectations in the mass range of 10-100M_{sun}_, but lacked spectroscopic measurements of the cluster. We aim to provide spectroscopic evidence regarding the nature of the putative star cluster in Eridanus 2 and to place constraints on MACHOs as a constituent of dark matter. We present spectroscopic observations of the central square arcminute of Eridanus 2 from MUSE-Faint, a survey of ultrafaint dwarf galaxies with the Multi Unit Spectroscopic Explorer on the Very Large Telescope. We derived line-of-sight velocities for possible member stars of the putative cluster and for stars in the centre of Eridanus 2. We discuss the existence of the cluster and determine new constraints for MACHOs using the Fokker-Planck diffusion approximation. Out of 182 extracted spectra, we identify 26 member stars of Eridanus 2, seven of which are possible cluster members. We find intrinsic mean line-of-sight velocities of 79.7^+3.1^_3.8_km/s and 76.0^+3.2^_3.7_km/s for the cluster and the bulk of Eridanus 2, respectively, as well as intrinsic velocity dispersions of <7.6km/s (68-% upper limit) and 10.3^+3.9^_3.2_km/s, respectively. This indicates that the cluster most likely exists as a distinct dynamical population hosted by Eridanus 2 and that it does not have a surplus of dark matter over the background distribution. Among the member stars in the bulk of Eridanus 2, we find possible carbon stars, alluding to the existence of an intermediate-age population.We derived constraints on the fraction of dark matter that can consist of MACHOs with a given mass between 1-10^5^M_{sun}_. For dark matter consisting purely of MACHOs, the mass of the MACHOs must be less than 7.6M_{sun}_ and 44M_{sun}_ at a 68- and 95-% confidence level, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/708/560
- Title:
- Spectroscopy of UMa II and Coma Ber
- Short Name:
- J/ApJ/708/560
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectra of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way (MW), Ursa Major II, and Coma Berenices obtained with the Keck/High Resolution Echelle Spectrometer (HIRES). These observations include the first high-resolution spectroscopic observations of extremely metal-poor ([Fe/H]<-3.0) stars not belonging to the MW halo field star population. We obtain abundance measurements and upper limits for 26 elements between carbon and europium. The entire sample of stars spans a range of -3.2<[Fe/H]<-2.3, and we confirm that each galaxy contains a large intrinsic spread of Fe abundances. A comparison with MW halo stars of similar metallicities reveals substantial agreement between the abundance patterns of the ultra-faint dwarf galaxies and the MW halo for the light, {alpha}, and iron-peak elements (C to Zn). The abundances of neutron-capture elements (Sr to Eu) in the ultra-faint dwarf galaxies are extremely low, consistent with the most metal-poor halo stars, but not with the typical halo abundance pattern at [Fe/H]>~-3.0. Not only are our results broadly consistent with a galaxy formation model that predicts that massive dwarf galaxies are the source of the metal-rich component ([Fe/H]>-2.5) of the MW halo, but they also suggest that the faintest known dwarfs may be the primary contributors to the metal-poor end of the MW halo metallicity distribution.
1598. Spectroscopy of ups Sgr
- ID:
- ivo://CDS.VizieR/J/BaltA/21/219
- Title:
- Spectroscopy of ups Sgr
- Short Name:
- J/BaltA/21/219
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high resolution spectra of hydrogen-deficient binary {upsilon} Sgr are analyzed. The atmospheric parameters are T_eff_= 12300+/-200K, logg=2.5+/-0.5 and {xi}_t_=5-15km/s depending on the element.
- ID:
- ivo://CDS.VizieR/J/AJ/146/70
- Title:
- Spectroscopy of W UMa-type binary stars
- Short Name:
- J/AJ/146/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study is the first attempt to determine the metallicities of W UMa-type binary stars using spectroscopy. We analyzed about 4500 spectra collected at the David Dunlap Observatory. To circumvent problems caused by the extreme spectral line broadening and blending and by the relatively low quality of the data, all spectra were subject to the same broadening function (BF) processing to determine the combined line strength in the spectral window centered on the Mg I triplet between 5080{AA} and 5285{AA}. All individual integrated BFs were subsequently orbital-phase averaged to derive a single line-strength indicator for each star. The star sample was limited to 90 W UMa-type (EW) binaries with the strict phase-constancy of colors and without spectral contamination by spectroscopic companions. The best defined results were obtained for an F-type sub-sample (0.32<(B-V)_0_<0.62) of 52 binaries for which integrated BF strengths could be interpolated in the model atmosphere predictions. The logarithmic relative metallicities, [M/H], for the F-type sub-sample indicate metal abundances roughly similar to the solar metallicity, but with a large scatter which is partly due to combined random and systematic errors. Because of the occurrence of a systematic color trend resulting from inherent limitations in our approach, we were forced to set the absolute scale of metallicities to correspond to that derived from the m_1_index of the Stromgren uvby photometry for 24 binaries of the F-type sub-sample. The trend-adjusted metallicities [M/H]_1_ are distributed within -0.65<[M/H]_1_<+0.50, with the spread reflecting genuine metallicity differences between stars. One half of the F-sub-sample binaries have [M/H]_1_within -0.37<[M/H]_1_<+0.10, a median of -0.04 and a mean of -0.10, with a tail toward low metallicities, and a possible bias against very high metallicities. A parallel study of kinematic data, utilizing the most reliable and recently obtained proper motion and radial velocity data for 78 binaries of the full sample, shows that the F-type sub-sample binaries (44 stars with both velocities and metallicity determinations) have similar kinematic properties to solar-neighborhood, thin-disk dwarfs with space velocity component dispersions: {sigma}U=33km/s, {sigma}V=23km/s and {sigma}W=14km/s. FU Dra with a large spatial velocity, V_tot_=197km/s and [M/H]_1_=-0.6+/-0.2, appears to be the only thick-disk object in the F-type sub-sample. The kinematic data indicate that the F-type EW binaries are typical, thin-disk population stars with ages about 3-5.5Gyr. The F-type binaries that appear to be older than the rest tend to have systematically smaller mass ratios than most of the EW binaries of the same period.
- ID:
- ivo://CDS.VizieR/J/ApJ/749/124
- Title:
- Spectroscopy on LMC clusters
- Short Name:
- J/ApJ/749/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As part of an ongoing program to measure detailed chemical abundances in nearby galaxies, we use a sample of young- to intermediate-age clusters in the Large Magellanic Cloud with ages of 10Myr-2Gyr to evaluate the effect of isochrone parameters, specifically core convective overshooting, on Fe abundance results from high-resolution, integrated light spectroscopy. In this work we also obtain fiducial Fe abundances from high-resolution spectroscopy of the cluster individual member stars. We compare the Fe abundance results for the individual stars to the results from isochrones and integrated light spectroscopy to determine whether isochrones with convective overshooting should be used in our integrated light analysis of young- to intermediate-age (10Myr-3Gyr) star clusters. We find that when using the isochrones from the Teramo group, we obtain more accurate results for young- and intermediate-age clusters over the entire age range when using isochrones without convective overshooting. While convective overshooting is not the only uncertain aspect of stellar evolution, it is one of the most readily parameterized ingredients in stellar evolution models, and thus important to evaluate for the specific models used in our integrated light analysis. This work demonstrates that our method for integrated light spectroscopy of star clusters can provide unique tests for future constraints on stellar evolution models of young- and intermediate-age clusters.