- ID:
- ivo://CDS.VizieR/J/ApJ/808/103
- Title:
- Kapteyn moving group star abundances
- Short Name:
- J/ApJ/808/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Kapteyn moving group has been postulated as tidal debris from {omega} Centauri. If true, members of the group should show some of the chemical abundance patterns known for stars in the cluster. We present an optical and near-infrared high-resolution, high-signal-to-noise ratio spectroscopic study of 14 stars of the Kapteyn group, plus 10 additional stars (the {omega} Cen group) that, while not listed as members of the Kapteyn group as originally defined, have nevertheless been associated dynamically with {omega} Centauri. Abundances for Na, O, Mg, Al, Ca, and Ba were derived from the optical spectra, while the strength of the chromospheric HeI10830{AA} line is studied as a possible helium abundance indicator. The resulting Na-O and Mg-Al patterns for stars of the combined Kapteyn and {omega} Cen group samples do not resemble those of {omega} Centauri, and are not different from those of field stars of the Galactic halo. The distribution of equivalent widths of the HeI10830{AA} line is consistent with that found among non-active field stars. Therefore, no evidence is found for second-generation stars within our samples, which most likely rules out a globular-cluster origin. Moreover, no hint of the unique barium overabundance at the metal-rich end, well established for {omega} Centauri stars, is seen among stars of the combined samples. Because this specific Ba pattern is present in {omega} Centauri irrespective of stellar generation, this would rule out the possibility that our entire sample might be composed of only first-generation stars from the cluster. Finally, for the stars of the Kapteyn group, the possibility of an origin in the hypothetical parent galaxy of {omega} Centauri is disfavored by the different run of {alpha}-elements with metallicity between our targets and stars from present-day dwarf galaxies.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/360/587
- Title:
- K-band imaging of H{delta}-strong galaxies
- Short Name:
- J/MNRAS/360/587
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present UFTI K-band imaging observations of 222 galaxies that are selected from the Sloan Digital Sky Survey to have unusually strong H{delta} absorption equivalent widths, W(H{delta})>4{AA}. Using GIM2D, the images are fitted with two-dimensional surface-brightness models consisting of a simple disc and bulge component to derive the fraction of luminosity in the bulge B/T.
- ID:
- ivo://CDS.VizieR/J/ApJ/748/93
- Title:
- K-band spectra for 133 nearby M dwarfs
- Short Name:
- J/ApJ/748/93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present K-band spectra for 133 nearby (d < 33 pc) M dwarfs, including 18 M dwarfs with reliable metallicity estimates (as inferred from an FGK type companion), 11 M dwarf planet hosts, more than 2/3 of the M dwarfs in the northern 8 pc sample, and several M dwarfs from the LSPM catalog. From these spectra, we measure equivalent widths of the Ca and Na lines, and a spectral index quantifying the absorption due to H_2_O opacity (the H_2_O-K2 index). Using empirical spectral type standards and synthetic models, we calibrate the H_2_O-K2 index as an indicator of an M dwarf's spectral type and effective temperature. We also present a revised relationship that estimates the [Fe/H] and [M/H] metallicities of M dwarfs from their Na I, Ca I, and H_2_O-K2 measurements. Comparisons to model atmosphere provide a qualitative validation of our approach, but also reveal an overall offset between the atomic line strengths predicted by models as compared to actual observations. Our metallicity estimates also reproduce expected correlations with Galactic space motions and H{alpha} emission line strengths, and return statistically identical metallicities for M dwarfs within a common multiple system. Finally, we find systematic residuals between our H_2_O-based spectral types and those derived from optical spectral features with previously known sensitivity to stellar metallicity, such as TiO, and identify the CaH1 index as a promising optical index for diagnosing the metallicities of near-solar M dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/471
- Title:
- Keck DEIMOS spectroscopy of GALEX sources
- Short Name:
- J/ApJS/173/471
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report results from a pilot program to obtain spectroscopy for objects detected in the Galaxy Evolution Explorer (GALEX) Medium Imaging Survey (MIS). Our study examines the properties of galaxies detected by GALEX fainter than the Sloan Digital Sky Survey (SDSS) spectroscopic survey. This is the first study to extend the techniques of Salim and coworkers to estimate stellar masses, star formation rates (SFRs), and the b (star formation history) parameter for star-forming galaxies out to z~0.7. We obtain redshifts for 50 GALEX MIS sources reaching NUV=23.9 (AB mag) having counterparts in the SDSS Data Release 4 (DR4). Of our sample, 43 are star-forming galaxies with z<0.7, 3 have emission-line ratios indicative of active galactic nuclei with z<0.7, and 4 objects with z>1 are QSOs, 3 of which are not previously cataloged. We compare our sample to a much larger sample of ~50000 matched GALEX/SDSS galaxies with SDSS spectroscopy; while our survey is shallow, the optical counterparts to our sources reach ~3mag fainter in SDSS r than the SDSS spectroscopic sample. We use emission-line diagnostics for the galaxies to determine that the sample contains mostly star-forming galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/860/109
- Title:
- Keck HIRES obs. of 245 subgiants (retired A stars)
- Short Name:
- J/ApJ/860/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Exoplanet surveys of evolved stars have provided increasing evidence that the formation of giant planets depends not only on stellar metallicity ([Fe/H]) but also on the mass (M*). However, measuring accurate masses for subgiants and giants is far more challenging than it is for their main-sequence counterparts, which has led to recent concerns regarding the veracity of the correlation between stellar mass and planet occurrence. In order to address these concerns, we use HIRES spectra to perform a spectroscopic analysis on a sample of 245 subgiants and derive new atmospheric and physical parameters. We also calculate the space velocities of this sample in a homogeneous manner for the first time. When reddening corrections are considered in the calculations of stellar masses and a -0.12M_{sun}_ offset is applied to the results, the masses of the subgiants are consistent with their space velocity distributions, contrary to claims in the literature. Similarly, our measurements of their rotational velocities provide additional confirmation that the masses of subgiants with M*>=1.6M_{sun}_ (the "retired A stars") have not been overestimated in previous analyses. Using these new results for our sample of evolved stars, together with an updated sample of FGKM dwarfs, we confirm that giant planet occurrence increases with both stellar mass and metallicity up to 2.0M_{sun}_. We show that the probability of formation of a giant planet is approximately a one-to-one function of the total amount of metals in the protoplanetary disk M* 10^[Fe/H]. This correlation provides additional support for the core accretion mechanism of planet formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/123
- Title:
- Keck Lyman continuum spectroscopic survey (KLCS)
- Short Name:
- J/ApJ/869/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a deep spectroscopic survey quantifying the statistics of the escape of ionizing radiation from star-forming galaxies at z~3. We measure the ratio of ionizing to non-ionizing UV flux density <f_900_/f_1500_>_obs_, where f_900_ is the mean flux density evaluated over the range [880,910]{AA}. We quantify the emergent ratio of ionizing to non-ionizing UV flux density by analyzing high signal-to-noise ratio composite spectra formed from subsamples with common observed properties and numbers sufficient to reduce the statistical uncertainty in the modeled IGM+CGM correction to obtain precise values of <f_900_/f_1500_>_out_, including a full-sample average <f_900_/f_1500>_out_=0.057{+/-}0.006. We show that <f_900_/f_1500_>_out_ increases monotonically with W_{lambda}_(Ly{alpha}), inducing an inverse correlation with UV luminosity as a by-product. We fit the composite spectra using stellar spectral synthesis together with models of the ISM in which a fraction f_c_ of the stellar continuum is covered by gas with column density N_HI_. We show that the composite spectra simultaneously constrain the intrinsic properties of the stars (L_900_/L_1500_)_int_ along with f_c_, N_HI_, E(B-V), and f_esc,abs_, the absolute escape fraction of ionizing photons. We find a sample-averaged f_esc,abs_=0.09{+/-}0.01, with subsamples falling along a linear relation <f_esc,abs_>~0.75[W_{lambda}_(Ly{alpha})/110{AA}]. Using the far-UV luminosity function, the distribution function n(W(Ly{alpha})), and the relationship between W_{lambda}_(Ly{alpha}) and <f_900_/f_1500_>_out_, we estimate the total ionizing emissivity of z~3 star-forming galaxies with M_uv_<=-19.5, which exceeds the contribution of quasi-stellar objects by a factor of ~3, and accounts for ~50% of the total {epsilon}LyC at z~3 estimated using indirect methods.
- ID:
- ivo://CDS.VizieR/J/MNRAS/494/2429
- Title:
- Kinematics of nearby young stars
- Short Name:
- J/MNRAS/494/2429
- Date:
- 19 Nov 2021 14:22:11
- Publisher:
- CDS
- Description:
- In the last three decades several hundred nearby members of young stellar moving groups (MGs) have been identified, but there has been less systematic effort to quantify or characterize young stars that do not belong to previously identified MGs. Using a kinematically unbiased sample of 225 lithium-rich stars within 100 pc, we find that only 50+/-10 per cent of young (<=125Myr), low-mass (0.5<M/M_{sun}_<1.0) stars, are kinematically associated with known MGs. Whilst we find some evidence that five of the non-MG stars may be connected with the Lower Centaurus-Crux association, the rest form a kinematically 'hotter' population, much more broadly dispersed in velocity, and with no obvious concentrations in space. The mass distributions of the MG members and non-MG stars are similar, but the non-MG stars may be older on average. We briefly discuss several explanations for the origin of the non-MG population.
- ID:
- ivo://CDS.VizieR/J/A+A/563/A94
- Title:
- Kinematics of the Gamma Vel cluster
- Short Name:
- J/A+A/563/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A key science goal of the Gaia-ESO survey (GES) at the VLT is to use the kinematics of low-mass stars in young clusters and star forming regions to probe their dynamical histories and how they populate the field as they become unbound. The clustering of low-mass stars around the massive Wolf-Rayet binary system {gamma}^2^ Velorum was one of the first GES targets. Targets were selected from colour-magnitude diagrams and intermediate resolution spectroscopy was used to derive radial velocities and assess membership from the strength of the LiI 6708{AA} line. The radial velocity distribution was analysed using a maximum likelihood technique that accounts for unresolved binaries.
- ID:
- ivo://CDS.VizieR/J/AJ/130/496
- Title:
- KISS emission-line galaxy candidates
- Short Name:
- J/AJ/130/496
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopic observations for 315 emission-line galaxy (ELG) candidates from the KPNO International Spectroscopic Survey (KISS) have been obtained using the MDM Observatory 2.4m telescope on Kitt Peak. KISS is a wide-field objective-prism survey for extragalactic emission-line objects that has cataloged over 2200 ELG candidates to date. Spectroscopic follow-up observations are being carried out to study the characteristics of the survey objects. The observational data presented here include redshifts, reddening estimates, line equivalent widths, H{alpha} line fluxes, and emission-line ratios. The galaxies have been classified based on their emission-line characteristics.
- ID:
- ivo://CDS.VizieR/J/AJ/130/2584
- Title:
- KISS emission-line galaxy candidates. IV
- Short Name:
- J/AJ/130/2584
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopic observations for 614 emission-line galaxy (ELG) candidates from the KPNO International Spectroscopic Survey (KISS) have been obtained using the KPNO 2.1m telescope and the WIYN 3.5m telescope. KISS is a wide-field objective-prism survey for extragalactic emission-line objects that has cataloged over 2400 ELG candidates to date. Spectroscopic follow-up observations are being carried out at several telescopes to study the characteristics of the survey objects. We present the following data derived from the KPNO spectra: redshifts, reddening estimates, line equivalent widths, H{alpha} line fluxes, and emission-line ratios. The galaxies have been classified based on their emission-line characteristics.
