- ID:
- ivo://CDS.VizieR/J/AcA/63/379
- Title:
- OGLE-III variable stars in Galactic disk area
- Short Name:
- J/AcA/63/379
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for pulsating stars in the 7.12deg^2^ OGLE-III Galactic disk area in the direction tangent to the Centaurus Arm. We report the identification of 20 Classical Cepheids, 45 RR Lyr type stars, 31 Long-Period Variables, such as Miras and Semi-Regular Variables, one pulsating white dwarf, and 58 very likely {delta} Sct type stars. Based on asteroseismic models constructed for one quadruple-mode and six triple-mode {delta} Sct type pulsators, we estimated masses, metallicities, ages, and distance moduli to these objects. The modeled stars have masses in the range 0.9-2.5M_{sun}_ and are located at distances between 2.5kpc and 6.2kpc. Two triple-mode and one double-mode pulsators seem to be Population II stars of the SX Phe type, probably from the Galactic halo. Our sample also includes candidates for Type II Cepheids and unclassified short-period (P<0.23d) multi-mode stars which could be either {delta}Sct or {beta}Cep type stars. One of the detected variables is a very likely {delta} Sct star with an exceptionally high peak-to-peak I-band amplitude of 0.35mag at the very short period of 0.0196d. All reported pulsating variable stars but one object are new discoveries. They are included in the OGLE-III Catalog of Variable Stars. Finally, we introduce the on-going OGLE-IV Galactic Disk Survey, which covers more than half of the Galactic plane. For the purposes of future works on the spiral structure and star formation history of the Milky Way, we have already compiled a list of known Galactic Classical Cepheids.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/109/489
- Title:
- OH observations of Arecibo OH/IR stars
- Short Name:
- J/ApJS/109/489
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Arecibo 1612MHz survey of a complete sample of color-selected IRAS sources with 25{mu}m fluxes S(25)>2 Jy detected 393 OH/IR stars. A complementary 1667 and 1665MHz OH survey of these objects is presented here. Main-line masers have been detected in 238 surveyed objects: 18 exhibit only 1665MHz emission, 220 exhibit 1667MHz masers, and 119 exhibit both. The main lines were not detected in 159 objects.
- ID:
- ivo://CDS.VizieR/J/AJ/123/2772
- Title:
- OH-selected AGB and post-AGB objects. I.
- Short Name:
- J/AJ/123/2772
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using 766 compact objects found in a systematic survey of the Galactic plane in the 1612MHz masing OH line, new light is cast on the IR properties of evolved stars on the thermally pulsing asymptotic giant branch (AGB) and beyond. The usual mid-IR selection criteria for post-AGB, based on IRAS colors, largely fail to distinguish early post-AGB stages. A two-color diagram from much narrower band MSX flux densities, with bimodal distributions, provides a better tool for doing this. Four mutually consistent selection criteria for OH-masing red protoplanetary nebulae are given, as well as two for early post-AGB masers and one for all post-AGB masers including the earliest ones. All these criteria miss a group of blue, high-outflow post-AGB sources with 60{mu}m excess; these will be discussed in detail in Paper II (Sevenster, 2002AJ....123.2772S). The majority of post-AGB sources show regular double-peaked spectra in the OH 1612MHz line, with fairly low outflow velocities, although the fractions of single peaks and irregular spectra may vary with age and mass. The OH flux density shows a fairly regular relation with the stellar flux and the envelope optical depth, with the maser efficiency increasing with IRAS color R_21_. The OH flux density is linearly correlated with the 60{mu}m flux density.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/163
- Title:
- OI abs. search in Keck and VLT spectra of 199 QSOs
- Short Name:
- J/ApJ/883/163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey for metal absorption systems traced by neutral oxygen over 3.2<z<6.5. Our survey uses Keck/ESI and VLT/X-Shooter spectra of 199 QSOs with redshifts up to 6.6. In total, we detect 74 OI absorbers, of which 57 are separated from the background QSO by more than 5000km/s. We use a maximum likelihood approach to fit the distribution of OI{lambda}1302 equivalent widths in bins of redshift and from this determine the evolution in number density of absorbers with W_1302_>0.05{AA}, of which there are 49 nonproximate systems in our sample. We find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. The number density over 4.9<z<5.7 is a factor of 1.7-4.1 lower (68% confidence) than that over 5.7<z<6.5, with a lower value at z<5.7 favored with 99% confidence. This decrease suggests that the fraction of metals in a low-ionization phase is larger at z~6 than at lower redshifts. Absorption from highly ionized metals traced by CIV is also weaker in higher-redshift OI systems, supporting this picture. The evolution of OI absorbers implies that metal-enriched circumgalactic gas at z~6 is undergoing an ionization transition driven by a strengthening ultraviolet background. This in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/13
- Title:
- OI equivalent widths in Be stars
- Short Name:
- J/ApJ/753/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The possibility of the Ly{beta} fluorescence mechanism being operational in classical Be (CBe) stars and thereby contributing to the strength of the OI{lambda}8446 line has been recognized for long. However, this supposition needs to be quantified by comparing observed and predicted OI line ratios. In the present work, optical and near-infrared spectra of CBe stars are presented. We analyze the observed strengths of the OI{lambda}7774, {lambda}8446, {lambda}11287, and {lambda}13165 lines, which have been theoretically proposed as diagnostics for identifying the excitation mechanism. We have considered and examined the effects of Ly{beta} fluorescence, collisional excitation, recombination, and continuum fluorescence on these O I line strengths. From our analysis it appears that the Ly{beta} fluorescence process is indeed operative in Be stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/872/55
- Title:
- OI, GeII, KrI & H abundances from HST UV spectra
- Short Name:
- J/ApJ/872/55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In a survey of archived ultraviolet spectra of 100 stars recorded by the echelle spectrograph of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we measure the strengths of the weak absorption features of OI, GeII, and KrI in the interstellar medium. Our objective is to undertake an investigation that goes beyond earlier abundance studies to see how these elements are influenced independently by three different environmental properties: (1) values of a generalized atomic depletion factor F_*_ due to condensations onto dust grains (revealed here by the abundances of Mg and Mn relative to H), (2) the fraction of H atoms in the form of H_2_/f(H_2_), and (3) the ambient intensity I of ultraviolet starlight relative to an average value in our part of the Galaxy I_0_. As expected, the gas-phase abundances of all three elements exhibit negative partial correlations with F*. The abundances of free O atoms show significant positive partial correlations with logf(H_2_) and log(I/I_0_), while Ge and Kr exhibit negative partial correlations with log(I/I_0_) at marginal levels of significance. After correcting for these trends, the abundances of O relative to H show no significant variations with location, except for the already-known radial gradient of light-element abundances in the Milky Way. A comparison of Ge and O abundances revealed no significant regional enhancements or deficiencies of neutron-capture elements relative to {alpha}-process ones.
- ID:
- ivo://CDS.VizieR/J/ApJ/799/205
- Title:
- [OII] emitting galaxies in the HETDEX survey
- Short Name:
- J/ApJ/799/205
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) pilot survey identified 284 [OII]{lambda}3727 emitting galaxies in a 169arcmin^2^ field of sky in the redshift range 0<z<0.57. This line flux limited sample provides a bridge between studies in the local universe and higher-redshift [OII] surveys. We present an analysis of the star formation rates (SFRs) of these galaxies as a function of stellar mass as determined via spectral energy distribution fitting. The [OII] emitters fall on the "main sequence" of star-forming galaxies with SFR decreasing at lower masses and redshifts. However, the slope of our relation is flatter than that found for most other samples, a result of the metallicity dependence of the [OII] star formation rate indicator. The mass-specific SFR is higher for lower mass objects, supporting the idea that massive galaxies formed more quickly and efficiently than their lower mass counterparts. This is confirmed by the fact that the equivalent widths of the [OII] emission lines trend smaller with larger stellar mass. Examination of the morphologies of the [OII] emitters reveals that their star formation is not a result of mergers, and the galaxies' half-light radii do not indicate evolution of physical sizes.
- ID:
- ivo://CDS.VizieR/J/AJ/95/1629
- Title:
- [O III] emission in 2 field-galaxy surveys
- Short Name:
- J/AJ/95/1629
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present emission-line strengths for 394 galaxies from the field-galaxy redshift surveys of Kirshner, Oemler, and Schechter (1978, Cat. <J/AJ/83/1549>, KOS) and Kirshner et al. (1983, Cat. <J/AJ/88/1285>, KOSS) as part of a study of the nature of field and void galaxies. These data are 95% complete in their coverage of the [O III]{lambda}{lambda}5007,4959 emission lines. We find that 8.8%+/-1.5% of a J magnitude-limited data set have [O III]{lambda}5007 emission equivalent widths greater than 10A. There is no evidence that the spatial distribution of emission-line galaxies in each field differs from that of galaxies without emission. However, there is a significant increase in the fraction of galaxies with strong [O III] emission in the southern fields of the Kirshner, Oemler, and Schechter (1978, Cat. <J/J/83/1549>) survey as compared with the other survey fields. Our results are consistent with the conclusion that the fraction of galaxies with emission is larger in the Bootes void than in the general field, but tighter constraints on the void normal galaxy population are needed to improve the statistics.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/1910
- Title:
- [OII] nebular emission from MgII absorbers
- Short Name:
- J/MNRAS/471/1910
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present nebular emission associated with 198 strong Mg II absorbers at 0.35<=z<=1.1 in the fibre spectra of quasars from the Sloan Digital Sky Survey. Measured [OII] luminosities (L_[OII]_) are typical of sub-L* galaxies with derived star formation rate (uncorrected for fibre losses and dust reddening) in the range of 0.5-20M_{sun}_/yr. Typically less than ~3 per cent of the MgII systems with rest equivalent width, W_2796_>=2{AA}, show L_[OII]_>=0.3L*_[OII]_. The detection rate is found to increase with increasing W_2796_ and z. No significant correlation is found between W_2796_ and L_[OII]_ even when we restrict the samples to narrow z ranges. A strong correlation is seen between L_[OII]_ and z. While this is expected from the luminosity evolution of galaxies, we show that finite fibre size plays a very crucial role in this correlation. The measured nebular line ratios (like [OIII]/[OII] and [OIII]/H {beta}) and their z evolution are consistent with those of galaxies detected in deep surveys. Based on the median stacked spectra, we infer the average metallicity (logZ~8.3), ionization parameter (logq~7.5) and stellar mass (log (M/M_{sun}_)~9.3). The MgII systems with nebular emission typically have W_2796_>=2{AA}, MgII doublet ratio close to 1 and W(FeII{lambda}2600)/W_2796_~0.5 as often seen in damped Ly {alpha} and 21-cm absorbers at these redshifts. This is the biggest reported sample of [OII] emission from MgII absorbers at low-impact parameters ideally suited for probing various feedback processes at play in z<=1 galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJS/94/687
- Title:
- Old stellar populations. V.
- Short Name:
- J/ApJS/94/687
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Twenty-one optical absorption features, 11 of which have been previously defined, are automatically measured in a sample of 460 stars. Following Gorgas et al., the indices are summarized in fitting functions that give index strengths as functions of stellar temperature, gravity, and [Fe/H]. This project was carried out with the purpose of predicting index strengths in the integrated light of stellar populations of different ages and metallicities, but the data should be valuable for stellar studies in the Galaxy as well. Several of the new indices appear to be promising indicators of metallicity for old stellar populations. A complete list of index data and atmospheric parameters is available in computer-readable form.
