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Start Over Subject optical astronomy
3481. Spectroscopy of ~100 G/K/M-type Sco-Cen complex members
ID:
ivo://CDS.VizieR/J/AJ/144/8
Title:
Spectroscopy of ~100 G/K/M-type Sco-Cen complex members
Short Name:
J/AJ/144/8
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have spectroscopically identified ~100 G-, K-, and M-type members of the Scorpius-Centaurus complex. To deduce the age of these young stars we compare their Li {lambda}6708 absorption line strengths against those of stars in the TW Hydrae association and {beta} Pictoris moving group. These line strengths indicate that Sco-Cen stars are younger than {beta} Pic stars whose ages of ~12Myr have previously been derived from a kinematic traceback analysis. Our derived age, ~10Myr, for stars in the Lower Centaurus Crux and Upper Centaurus Lupus subgroups of ScoCen is younger than previously published ages based on the moving cluster method and upper main-sequence fitting. The discrepant ages are likely due to an incorrect (or lack of) cross-calibration between model-dependent and model-independent age-dating methods.
3482. Spectroscopy of Grus II, Tuc IV and Tuc V
ID:
ivo://CDS.VizieR/J/ApJ/892/137
Title:
Spectroscopy of Grus II, Tuc IV and Tuc V
Short Name:
J/ApJ/892/137
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Magellan/IMACS spectroscopy of three recently discovered ultra-faint Milky Way satellites, Grus II, Tucana IV, and Tucana V. We measure systemic velocities of v_hel_=-110.0+/-0.5km/s, v_hel_=15.9_-1.7_^+1.8^km/s, and v_hel_=-36.2_-2.2_^+2.5^km/s for the three objects, respectively. Their large relative velocities demonstrate that the satellites are unrelated despite their close physical proximity. We determine a velocity dispersion for Tuc IV of {sigma}=4.3_-1.0_^+1.7^km/s, but we cannot resolve the velocity dispersions of the other two systems. For Gru II, we place an upper limit (90% confidence) on the dispersion of {sigma}<1.9km/s, and for Tuc V, we do not obtain any useful limits. All three satellites have metallicities below [Fe/H]=-2.1, but none has a detectable metallicity spread. We determine proper motions for each satellite based on Gaia astrometry and compute their orbits around the Milky Way. Gru II is on a tightly bound orbit with a pericenter of 25_-7_^+6^kpc and orbital eccentricity of 0.45_-0.05_^+0.08^. Tuc V likely has an apocenter beyond 100kpc and could be approaching the Milky Way for the first time. The current orbit of Tuc IV is similar to that of Gru II, with a pericenter of 25_-8_^+11^kpc and an eccentricity of 0.36_-0.06_^+0.13^. However, a backward integration of the position of Tuc IV demonstrates that it collided with the Large Magellanic Cloud at an impact parameter of 4kpc ~120Myr ago, deflecting its trajectory and possibly altering its internal kinematics. Based on their sizes, masses, and metallicities, we classify Gru II and Tuc IV as likely dwarf galaxies, but the nature of Tuc V remains uncertain.
3483. Spectroscopy of hot stars in the halo. III
ID:
ivo://CDS.VizieR/J/AJ/117/2329
Title:
Spectroscopy of hot stars in the halo. III
Short Name:
J/AJ/117/2329
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from an analysis of medium-resolution spectroscopy and UBV photometry for a sample of 1121 A-type stars in the halo (and disk) of the Galaxy. A previously developed calibration technique is used to assign estimates of effective temperature, surface gravity, and stellar metal abundance, as parametrized by [Fe/H]. Radial velocities are reported with an accuracy of {~}10 km.s^-1^. Distance estimates are obtained for the stars with well-determined luminosity classes. Note that although we refer to "A-type" stars, which dominate the present sample, the present data set includes roughly 100 stars of later spectral types, as a result of the temperature range we have chosen to explore in this paper (6000 K {<=} T_eff_ {<=} 10,000 K).
3484. Spectroscopy of low-metallicity star candidates
ID:
ivo://CDS.VizieR/J/ApJ/870/122
Title:
Spectroscopy of low-metallicity star candidates
Short Name:
J/ApJ/870/122
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from an observing campaign to identify low-metallicity stars in the Best & Brightest Survey. From medium-resolution (R~1200-2000) spectroscopy of 857 candidates, we estimate the stellar atmospheric parameters (T_eff_, logg, and [Fe/H]), as well as carbon and {alpha}-element abundances. We find that 69% of the observed stars have [Fe/H]<=-1.0, 39% have [Fe/H]<=-2.0, and 2% have [Fe/H]<=-3.0. There are also 133 carbon-enhanced metal-poor (CEMP) stars in this sample, with 97 CEMP Group I and 36 CEMP Group II stars identified in the A(C) versus [Fe/H] diagram. A subset of the confirmed low-metallicity stars were followed-up with high-resolution spectroscopy, as part of the R-process Alliance, with the goal of identifying new highly and moderately r-process-enhanced stars. Comparison between the stellar atmospheric parameters estimated in this work and from high-resolution spectroscopy exhibit good agreement, confirming our expectation that medium-resolution observing campaigns are an effective way of selecting interesting stars for further, more targeted, efforts.
3485. Spectroscopy of M31 globular clusters
ID:
ivo://CDS.VizieR/J/ApJ/769/10
Title:
Spectroscopy of M31 globular clusters
Short Name:
J/ApJ/769/10
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of an [OIII]{lambda}5007 spectroscopic survey for planetary nebulae (PNe) located within the star clusters of M31. By examining R~5000 spectra taken with the WIYN+Hydra spectrograph, we identify 3 PN candidates in a sample of 274 likely globular clusters, 2 candidates in objects which may be globular clusters, and 5 candidates in a set of 85 younger systems. The possible PNe are all faint, between ~2.5 and ~6.8mag down the PN luminosity function, and, partly as a consequence of our selection criteria, have high excitation, with [OIII]{lambda}5007 to H{beta} ratios ranging from 2 to >~12. We discuss the individual candidates, their likelihood of cluster membership, and the possibility that they were formed via binary interactions within the clusters. Our data are consistent with the suggestion that PN formation within globular clusters correlates with binary encounter frequency, though, due to the small numbers and large uncertainties in the candidate list, this study does not provide sufficient evidence to confirm the hypothesis.
3486. Spectroscopy of 462 nearby Type Ia supernovae
ID:
ivo://CDS.VizieR/J/AJ/143/126
Title:
Spectroscopy of 462 nearby Type Ia supernovae
Short Name:
J/AJ/143/126
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 2603 spectra of 462 nearby Type Ia supernovae (SNe Ia), including 2065 previously unpublished spectra, obtained during 1993-2008 through the Center for Astrophysics Supernova Program. There are on average eight spectra for each of the 313 SNe Ia with at least two spectra. Most of the spectra were obtained with the FAST spectrograph at the Fred Lawrence Whipple Observatory 1.5m telescope and reduced in a consistent manner, making this data set well suited for studies of SN Ia spectroscopic diversity. Using additional data from the literature, we study the spectroscopic and photometric properties of SNe Ia as a function of spectroscopic class using the classification schemes of Branch et al. (2006PASP..118..560B) and Wang et al. (2009, Cat. J/ApJ/699/L139). The width-luminosity relation appears to be steeper for SNe Ia with broader lines, although the result is not statistically significant with the present sample. Based on the evolution of the characteristic SiII{lambda}6355 line, we propose improved methods for measuring velocity gradients, revealing a larger range than previously suspected, from ~0 to ~400km/s/day considering the instantaneous velocity decline rate at maximum light.
3487. Spectroscopy of quiescent gal. in 9 lensing clusters
ID:
ivo://CDS.VizieR/J/ApJ/902/17
Title:
Spectroscopy of quiescent gal. in 9 lensing clusters
Short Name:
J/ApJ/902/17
Date:
03 Mar 2022 11:35:20
Publisher:
CDS
Description:
We measure the central stellar velocity dispersion function for quiescent galaxies in a set of nine northern clusters in the redshift range 0.18<z<0.29 and with strong lensing arcs in Hubble Space Telescope images. The velocity dispersion function links galaxies directly to their dark matter halos. From dense SDSS and MMT/Hectospec spectroscopy, we identify 222-463 spectroscopic members in each cluster. We derive physical properties of cluster members including redshift, D_n_4000, and central stellar velocity dispersion and we include a table of these measurements for 3419 cluster members. We construct the velocity dispersion functions for quiescent galaxies with D_n_4000>1.5 and within R200. The cluster velocity dispersion functions all show excesses at {sigma}>~250km/s compared to the field velocity dispersion function. The velocity dispersion function slope at large velocity dispersion ({sigma}>160km/s) is steeper for more massive clusters, consistent with the trend observed for cluster luminosity functions. The spatial distribution of galaxies with large velocity dispersion at radii larger than R200 further underscores the probable major role of dry mergers in the growth of massive cluster galaxies during cluster assembly.
3488. Spectroscopy of Segue 1
ID:
ivo://CDS.VizieR/J/ApJ/692/1464
Title:
Spectroscopy of Segue 1
Short Name:
J/ApJ/692/1464
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Keck/DEIMOS spectroscopy of Segue 1, an ultra-low-luminosity (M_V_=-1.5^+0.6^_-0.8_) Milky Way satellite companion. While the combined size and luminosity of Segue 1 are consistent with either a globular cluster or a dwarf galaxy, we present spectroscopic evidence that this object is a dark matter-dominated dwarf galaxy. We identify 24 stars as members of Segue 1 with a mean heliocentric recession velocity of 206+/-1.3km/s. Although Segue 1 spatially overlaps the leading arm of the Sagittarius stream, its velocity is 100km/s different from that predicted for recent Sagittarius tidal debris at this position. Using spectral synthesis modeling, we derive a metallicity for the single red giant branch star in our sample of [Fe/H]=-3.3+/-0.2dex. We conclude that Segue 1 is the least luminous of the ultra-faint galaxies recently discovered around the Milky Way, and is thus the least-luminous known galaxy.
3489. Spectroscopy of the fields of gravitational lenses
ID:
ivo://CDS.VizieR/J/ApJ/850/94
Title:
Spectroscopy of the fields of gravitational lenses
Short Name:
J/ApJ/850/94
Date:
21 Oct 2021
Publisher:
CDS
Description:
Strong gravitational lensing provides an independent measurement of the Hubble parameter (H_0_). One remaining systematic is a bias from the additional mass due to a galaxy group at the lens redshift or along the sightline. We quantify this bias for more than 20 strong lenses that have well-sampled sightline mass distributions, focusing on the convergence {kappa} and shear {gamma}. In 23% of these fields, a lens group contributes >=1% convergence bias; in 57%, there is a similarly significant line-of-sight group. For the nine time-delay lens systems, H0 is overestimated by 11_-2_^+3^% on average when groups are ignored. In 67% of fields with total {kappa}>=0.01, line-of-sight groups contribute >~2x more convergence than do lens groups, indicating that the lens group is not the only important mass. Lens environment affects the ratio of four (quad) to two (double) image systems; all seven quads have lens groups while only 3 of 10 doubles do, and the highest convergences due to lens groups are in quads. We calibrate the {gamma}-{kappa} relation: log({kappa}_tot_)=(1.94+/-0.34)log({gamma}_tot_)+(1.31+/-0.49) with an rms scatter of 0.34dex. Although shear can be measured directly from lensed images, unlike convergence, it can be a poor predictor of convergence; for 19% of our fields, {kappa} is >~2{gamma}. Thus, accurate cosmology using strong gravitational lenses requires precise measurement and correction for all significant structures in each lens field.
3490. Spectroscopy of the Galactic bar. I.
ID:
ivo://CDS.VizieR/J/ApJ/691/1387
Title:
Spectroscopy of the Galactic bar. I.
Short Name:
J/ApJ/691/1387
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use Fabry-Perot absorption line imaging spectroscopy to measure radial velocities using the CaII line in 3360 stars toward three lines of sight in the Milky Way's bar: Baade's Window and offset position at (l,b)~(+/-5.0,-3.5{deg}). This sample includes 2488 bar red clump giants, 339 bar M/K-giants, and 318 disk main-sequence stars. We measure the first four moments of the stellar velocity distribution of the red clump giants, and find it to be symmetric and flat-topped. We also measure the line-of-sight average velocity and dispersion of the red clump giants as a function of distance in the bar.