Search

Start Over Subject spectroscopy
1581. Measured atmospheric parameters of NGC6397 stars
ID:
ivo://CDS.VizieR/J/A+A/635/A161
Title:
Measured atmospheric parameters of NGC6397 stars
Short Name:
J/A+A/635/A161
Date:
21 Oct 2021
Publisher:
CDS
Description:
Recent work has used spectra of ~5000 stars in NGC 6397 that were extracted from a MUSE mosaic to determine the atmospheric parameters for these stars by fitting the spectra against the Goettingen Spectral Library. A significant change in metallicity between the turn off and the red giant branch was found and was discussed as a possible manifestation of predicted effects of atomic diffusion. However, the small amplitude of the effect and inconsistency with earlier measurements call for more attention before this result is interpreted. Systematic effects due to the interpolation or to the synthetic spectra cannot be ruled out at this level of precision. We reanalyze the data with : the ELODIE and MILES reference libraries in order to assess the robustness of the result. These empirical libraries have a finer metallicity coverage down to approximately the cluster metallicity turn-off. Methods. We used the ULySS full-spectrum fitting package, together with the library interpolators to remeasure the three atmospheric parameters effective temperature, surface gravity, and [Fe/H] metallicity. We find a very low [Fe/H] dispersion along the isochrone (0.07dex), consistent with our error estimate (0.05dex). However, the [Fe/H] trend is not reproducible. This shows that the data have the potential to reveal patterns of the magnitude of the expected physical effects, but the analysis methods need to be refined to cull systematic effects that currently dominate the patterns.
1582. MEGaSaURA. II. Stacked spectra
ID:
ivo://CDS.VizieR/J/ApJ/853/87
Title:
MEGaSaURA. II. Stacked spectra
Short Name:
J/ApJ/853/87
Date:
21 Oct 2021
Publisher:
CDS
Description:
We stack the rest-frame ultraviolet spectra of N=14 highly magnified gravitationally lensed galaxies at redshifts 1.6<z<3.6. The resulting new composite spans 900<{lambda}_rest_<3000{AA}, with a peak signal-to-noise ratio (S/N) of 103 per spectral resolution element (~100km/s). It is the highest S/N, highest spectral resolution composite spectrum of z~2-3 galaxies yet published. The composite reveals numerous weak nebular emission lines and stellar photospheric absorption lines that can serve as new physical diagnostics, particularly at high redshift with the James Webb Space Telescope (JWST). We report equivalent widths to aid in proposing for and interpreting JWST spectra. We examine the velocity profiles of strong absorption features in the composite, and in a matched composite of z~0 COS/HST galaxy spectra. We find remarkable similarity in the velocity profiles at z~0 and z~2, suggesting that similar physical processes control the outflows across cosmic time. While the maximum outflow velocity depends strongly on ionization potential, the absorption-weighted mean velocity does not. As such, the bulk of the high- ionization absorption traces the low-ionization gas, with an additional blueshifted absorption tail extending to at least -2000km/s. We interpret this tail as arising from the stellar wind and photospheres of massive stars. Starburst99 models are able to replicate this high-velocity absorption tail. However, these theoretical models poorly reproduce several of the photospheric absorption features, indicating that improvements are needed to match observational constraints on the massive stellar content of star-forming galaxies at z~2.
1583. MEGaSaURA. I. The sample and the spectra
ID:
ivo://CDS.VizieR/J/AJ/155/104
Title:
MEGaSaURA. I. The sample and the spectra
Short Name:
J/AJ/155/104
Date:
21 Oct 2021
Publisher:
CDS
Description:
We introduce Project MEGaSaURA: the Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas. MEGaSaURA comprises medium-resolution, rest-frame ultraviolet spectroscopy of N=15 bright gravitationally lensed galaxies at redshifts of 1.68<z<3.6, obtained with the MagE spectrograph on the Magellan telescopes. The spectra cover the observed-frame wavelength range 3200<{lambda}_o_<8280{AA}; the average spectral resolving power is R=3300. The median spectrum has a signal-to- noise ratio (S/N)=21 per resolution element at 5000{AA}. As such, the MEGaSaURA spectra have superior S/N and wavelength coverage compared to what COS/HST provides for starburst galaxies in the local universe. This paper describes the sample, the observations, and the data reduction. We compare the measured redshifts for the stars, the ionized gas as traced by nebular lines, and the neutral gas as traced by absorption lines; we find the expected bulk outflow of the neutral gas, and no systemic offset between the redshifts measured from nebular lines and the redshifts measured from the stellar continuum.
1584. 126 member galaxies of A780 radial velocities
ID:
ivo://CDS.VizieR/J/A+A/658/A159
Title:
126 member galaxies of A780 radial velocities
Short Name:
J/A+A/658/A159
Date:
22 Feb 2022
Publisher:
CDS
Description:
Clusters of galaxies evolve and accrete mass, mostly from small galaxy systems. Our aim is to study the velocity field of the galaxy cluster Abell 780, which is known for the powerful radio source Hydra A at its center and where a spectacular X-ray tail associated with the galaxy LEDA 87445 has been discovered. Our analysis is based on the new spectroscopic data for hundreds of galaxies obtained with the Italian Telescopio Nazionale Galileo and the Very Large Telescope. We have constructed a redshift catalog of 623 galaxies and selected a sample of 126 cluster members. We analyze the internal structure of the cluster using a number of techniques. We estimate the mean redshift z=0.0545, the line-of-sight velocity dispersion {sigma}_v_~800km/s, and the dynamical mass M200~5.4x10^14^M_{sun}_. The global properties of Abell 780 are typical of relaxed clusters. On a smaller scale, we can detect the presence of a galaxy group associated with LEDA 87445 in projected phase space. The mean velocity and position of the center of the group agree well with the velocity and position of LEDA 87445. We estimate the following parameters of the collision. The group is characterized by a higher velocity relative to the main system. It is infalling at a rest frame velocity of V_rf_~+870km/s and lies at a projected distance D~1.1Mpc to the south, slightly southeast of the cluster center. The mass ratio between the group and the cluster is ~1:5. We also find evidence of an asymmetry in the velocity distribution of galaxies in the inner cluster region, which might be related to a small low-velocity group detected as a substructure at V_rf_~-750km/s. We conclude that A780, although dynamically relaxed at first sight, contains small substructures that may have some impact on the energetics of the core region.
1585. Members for 20 open clusters
ID:
ivo://CDS.VizieR/J/A+A/643/A71
Title:
Members for 20 open clusters
Short Name:
J/A+A/643/A71
Date:
21 Oct 2021
Publisher:
CDS
Description:
Previous studies of open clusters have shown that lithium depletion is not only strongly age dependent but also shows a complex pattern with other parameters that is not yet understood. For pre- and main-sequence late-type stars, these parameters include metallicity, mixing mechanisms, convection structure, rotation, and magnetic activity. We perform a thorough membership analysis for a large number of stars observed within the Gaia-ESO survey (GES) in the field of 20 open clusters, ranging in age from young clusters and associations, to intermediate-age and old open clusters. Based on the parameters derived from the GES spectroscopic observations, we obtained lists of candidate members for each of the clusters in the sample by deriving RV distributions and studying the position of the kinematic selections in the EW(Li) versus Teff plane to obtain lithium members. We used gravity indicators to discard field contaminants and studied [Fe/H] metallicity to further confirm the membership of the candidates. We also made use of studies using recent data from the Gaia DR1 and DR2 releases to assess our member selections. We identified likely member candidates for the sample of 20 clusters observed in GES (iDR4) with UVES and GIRAFFE, and conducted a comparative study that allowed us to characterize the properties of these members, as well as identify field contaminant stars, both lithium-rich giants and non-giant outliers. This work is the first step towards the calibration of the lithium-age relation and its dependence on other GES parameters. During this project we aim to use this relation to infer the ages of GES field stars, and identify their potential membership to young associations and stellar kinematic groups of different ages.
1586. Membership in Ophiuchus & Upper Scorpius complex
ID:
ivo://CDS.VizieR/J/AJ/159/282
Title:
Membership in Ophiuchus & Upper Scorpius complex
Short Name:
J/AJ/159/282
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have performed a survey for new members of the Ophiuchus cloud complex using high-precision astrometry from the second data release of Gaia, proper motions measured with multi-epoch images from the Spitzer Space Telescope, and color-magnitude diagrams constructed with photometry from various sources. Through spectroscopy of candidates selected with those data, we have identified 155 new young stars. Based on available measurements of kinematics, we classify 102, 47, and 6 of those stars as members of Ophiuchus, Upper Sco, and other populations in Sco-Cen, respectively. We have also assessed the membership of all other stars in the vicinity of Ophiuchus that have spectroscopic evidence of youth from previous studies, arriving at a catalog of 373 adopted members of the cloud complex. For those adopted members, we have compiled mid-infrared photometry from Spitzer and the Wide-field Infrared Survey Explorer and have used mid-infrared colors to identify and classify circumstellar disks. We find that 210 of the members show evidence of disks, including 48 disks that are in advanced stages of evolution. Finally, we have estimated the relative median ages of the populations near the Ophiuchus clouds and the surrounding Upper Sco association using absolute K-band magnitudes (MK) based on Gaia parallaxes. If we adopt an age 10Myr for Upper Sco, then the relative values of MK imply median ages of ~2Myr for L1689 and embedded stars in L1688, 3-4Myr for low-extinction stars near L1688, and ~6Myr for the group containing {rho}Oph.
1587. Membership in the Cepheus association
ID:
ivo://CDS.VizieR/J/A+A/637/A43
Title:
Membership in the Cepheus association
Short Name:
J/A+A/637/A43
Date:
21 Oct 2021
Publisher:
CDS
Description:
Young field stars are hardly distinguishable from older ones because their space motion rapidly mixes them with the stellar population of the Galactic plane.Nevertheless, a careful target selection allows for young stars to be spotted throughout the sky. We aim to identify additional sources associated with the four young comoving stars that we discovered towards the CO Cepheus void and to provide a comprehensive view of the Cepheus association. Based on multivariate analysis methods, we have built an extended sample of 193 young star candidates, which are the optical and infrared counterparts of ROSAT All-Sky Survey and XMM-Newton X-ray sources. From optical spectroscopic observations, we measured their radial velocity with the cross-correlation technique. We derived their atmospheric parameters and projected rotational velocity with the code ROTFIT. We applied the subtraction of inactive templates to measure the lithium equivalent width, from which we infer their lithium abundance and age. Finally, we studied their kinematics using the second Gaia data release. Our sample is mainly composed of young or active stars and multiple systems. We identify two distinct populations of young stars that are spatially and kinematically separated. Those with an age between 100 and 300Myr are mostly projected towards the Galactic plane. In contrast, 23 of the 37 sources younger than 30Myr are located in the CO Cepheus void, and 21 of them belong to the stellar kinematic group that we previously reported in this sky area. We report a total of 32 bona fide members and nine candidates for this nearby (distance=157+/-10pc) young (age=10-20Myr) stellar association. According to the spatial distribution of its members, the original cluster is already dispersed and partially mixed with the local population of the Galactic plane.
1588. Members of the young open cluster IC 2395
ID:
ivo://CDS.VizieR/J/ApJ/832/87
Title:
Members of the young open cluster IC 2395
Short Name:
J/ApJ/832/87
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new deep UBVRI images and high-resolution multi-object optical spectroscopy of the young (~6-10Myr old), relatively nearby (800pc) open cluster IC 2395. We identify nearly 300 cluster members and use the photometry to estimate their spectral types, which extend from early B to middle M. We also present an infrared imaging survey of the central region using the IRAC and MIPS instruments on board the Spitzer Space Telescope, covering the wavelength range from 3.6 to 24{mu}m. Our infrared observations allow us to detect dust in circumstellar disks originating over a typical range of radii from ~0.1 to ~10 au from the central star. We identify 18 Class II, 8 transitional disk, and 23 debris disk candidates, respectively, 6.5%, 2.9%, and 8.3% of the cluster members with appropriate data. We apply the same criteria for transitional disk identification to 19 other stellar clusters and associations spanning ages from ~1 to ~18Myr. We find that the number of disks in the transitional phase as a fraction of the total with strong 24{mu}m excesses ([8]-[24]>=1.5) increases from (8.4+/-1.3)% at ~3Myr to (46+/-5)% at ~10Myr. Alternative definitions of transitional disks will yield different percentages but should show the same trend.
1589. Member stars in the MW satellite Tucana III
ID:
ivo://CDS.VizieR/J/ApJ/838/11
Title:
Member stars in the MW satellite Tucana III
Short Name:
J/ApJ/838/11
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite Tucana III (Tuc III). We identify 26 member stars in Tuc III from which we measure a mean radial velocity of v_hel_=-102.3+/-0.4(stat.)+/-2.0(sys.)km/s, a velocity dispersion of 0.1_-0.1_^+0.7^km/s, and a mean metallicity of [Fe/H]=-2.42_-0.08_^+0.07^. The upper limit on the velocity dispersion is {sigma}<1.5km/s at 95.5% confidence, and the corresponding upper limit on the mass within the half-light radius of Tuc III is 9.0x10^4^M_{sun}_. We cannot rule out mass-to-light ratios as large as 240M_{sun}_/L_{sun}_ for Tuc III, but much lower mass-to-light ratios that would leave the system baryon-dominated are also allowed. We measure an upper limit on the metallicity spread of the stars in Tuc III of 0.19dex at 95.5% confidence. Tuc III has a smaller metallicity dispersion and likely a smaller velocity dispersion than any known dwarf galaxy, but a larger size and lower surface brightness than any known globular cluster. Its metallicity is also much lower than those of the clusters with similar luminosity. We therefore tentatively suggest that Tuc III is the tidally stripped remnant of a dark matter-dominated dwarf galaxy, but additional precise velocity and metallicity measurements will be necessary for a definitive classification. If Tuc III is indeed a dwarf galaxy, it is one of the closest external galaxies to the Sun. Because of its proximity, the most luminous stars in Tuc III are quite bright, including one star at V=15.7 that is the brightest known member star of an ultra-faint satellite.
1590. Merged Log of IUE Observations
ID:
ivo://CDS.VizieR/VI/99
Title:
Merged Log of IUE Observations
Short Name:
VI/99
Date:
21 Oct 2021
Publisher:
CDS
Description:
The log contains a summary of all IUE Newly Extracted Spectra (INES), which resulted from a post-processing effort at Vilspa. It was constructed by using verified data from the IUE Final Archive Master Catalogue. The observations cover the whole life of the satellite, from March 1978 to September 1996.

Limit your search

more »

more »

more »

more »

more »