- ID:
- ivo://CDS.VizieR/J/ApJ/634/861
- Title:
- Old passively evolving galaxies at z=1
- Short Name:
- J/ApJ/634/861
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained the number counts and the rest-frame B-band luminosity function of color-selected old passively evolving galaxies (OPEGs) at z=1 with very high statistical accuracy using a large and homogeneous sample of about 4000 such objects with z'<25 detected in an area of 1.03deg^2^ in the Subaru/XMM-Newton Deep Survey (SXDS) field. Our selection criteria are defined on the i'-z' and R-z' color-magnitude plane so that OPEGs at z=0.9-1.1 with formation redshift z_f_=2-10 are properly sampled with minimum contamination by other populations. The limiting magnitude corresponds to the luminosity of galaxies with M*+3 at z=0 (where M* is the characteristic absolute magnitude of the Schechter galaxy luminosity function). We made pilot redshift observations for 99 OPEG candidates with 19<z'<22 and found that at least 78% (73 of 93) of the entire sample, or 95% (73 of 77) of those whose redshifts were obtained, indeed lie between z=0.87 and 1.12, and most of their spectra show a continuum break and strong Ca H and K lines, indicating that these objects are indeed dominated by the old stellar populations.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/722/1373
- Title:
- {omega} Centauri giants abundances
- Short Name:
- J/ApJ/722/1373
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present elemental abundances for 855 red giant branch (RGB) stars in the globular cluster Omega Centauri ({omega} Cen) from spectra obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. The sample includes nearly all RGB stars brighter than V=13.5 and spans {omega} Cen's full metallicity range. The heavy {alpha} elements (Si, Ca, and Ti) are generally enhanced by +/-0.3 dex and exhibit a metallicity-dependent morphology that may be attributed to mass and metallicity-dependent Type II supernova (SN) yields. The heavy {alpha} and Fe-peak abundances suggest minimal contributions from Type Ia SNe. The light elements (O, Na, and Al) exhibit >0.5 dex abundance dispersions at all metallicities, and a majority of stars with [Fe/H]>-1.6 have [O/Fe], [Na/Fe], and [Al/Fe] abundances similar to those in monometallic globular clusters, as well as O-Na, O-Al anticorrelations and the Na-Al correlation in all but the most metal-rich stars. A combination of pollution from intermediate-mass asymptotic giant branch stars and in situ mixing may explain the light element abundance patterns. A large fraction (27%) of {omega} Cen stars are O-poor ([O/Fe]<0) and are preferentially located within 5'-10' of the cluster center. The O-poor giants are spatially similar, located in the same metallicity range, and are present in nearly equal proportions to blue main-sequence stars. This suggests that the O-poor giants and blue main-sequence stars may share a common origin. [La/Fe] increases sharply at [Fe/H]>~-1.6, and the [La/Eu] ratios indicate that the increase is due to almost pure s-process production.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/59
- Title:
- Ophiuchus stellar stream with PS1 data
- Short Name:
- J/ApJ/809/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Ophiuchus stream is a recently discovered stellar tidal stream in the Milky Way. We present high-quality spectroscopic data for 14 stream member stars obtained using the Keck and MMT telescopes. We confirm the stream as a fast moving (v_los_~290km/s), kinematically cold group ({sigma}_{nu}_los__<~1km/s) of {alpha}-enhanced and metal-poor stars ([{alpha}/Fe]~0.4dex, [Fe/H]~-2.0dex). Using a probabilistic technique, we model the stream simultaneously in line-of-sight velocity, color-magnitude, coordinate, and proper motion space, and so determine its distribution in 6D phase-space. We find that the stream extends in distance from 7.5 to 9kpc from the Sun; it is 50 times longer than wide, merely appearing highly foreshortened in projection. The analysis of the stellar population contained in the stream suggests that it is ~12Gyr old, and that its initial stellar mass was ~2x10^4^M_{sun}_ (or at least >~7x10^3^M_{sun}_). Assuming a fiducial Milky Way potential, we fit an orbit to the stream that matches the observed phase-space distribution, except for some tension in the proper motions: the stream has an orbital period of ~350Myr, and is on a fairly eccentric orbit (e~0.66) with a pericenter of ~3.5kpc and an apocenter of ~17kpc. The phase-space structure and stellar population of the stream show that its progenitor must have been a globular cluster that was disrupted only ~240Myr ago. We do not detect any significant overdensity of stars along the stream that would indicate the presence of a progenitor, and conclude that the stream is all that is left of the progenitor.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/115
- Title:
- Optical follow-up of ASAS-SN M dwarf flares
- Short Name:
- J/ApJ/876/115
- Date:
- 18 Jan 2022 15:06:46
- Publisher:
- CDS
- Description:
- The All-sky Automated Survey for Supernovae (ASAS-SN) is the only project in existence to scan the entire sky in optical light approximately every day, reaching a depth of g~18mag. Over the course of its first 4yr of transient alerts (2013-2016), ASAS-SN observed 53 events classified as likely M dwarf flares. We present follow-up photometry and spectroscopy of all 53 candidates, confirming flare events on 47 M dwarfs, one K dwarf, and one L dwarf. The remaining four objects include a previously identified T Tauri star, a young star with outbursts, and two objects too faint to confirm. A detailed examination of the 49 flare star light curves revealed an additional six flares on five stars, resulting in a total of 55 flares on 49 objects ranging in V-band contrast from {Delta}V=-1 to -10.2mag. Using an empirical flare model to estimate the unobserved portions of the flare light curve, we obtain lower limits on the V-band energy emitted during each flare, spanning log(E_V_/erg)=32-35, which are among the most energetic flares detected on M dwarfs. The ASAS-SN M dwarf flare stars show a higher fraction of H{alpha} emission, as well as stronger H{alpha} emission, compared to M dwarfs selected without reference to activity, consistent with belonging to a population of more magnetically active stars. We also examined the distribution of tangential velocities, finding that the ASAS-SN flaring M dwarfs are likely to be members of the thin disk and are neither particularly young nor old.
- ID:
- ivo://CDS.VizieR/J/ApJ/723/1542
- Title:
- Optical high-resolution spectroscopy of WTTSs
- Short Name:
- J/ApJ/723/1542
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution spectroscopic observations for a sample of 19 weak-line T Tauri stars (WTTSs). Based on these observations and data of 108 WTTSs taken from the literature, we derive lithium abundances for 127 WTTSs. Investigation of a possible relation between lithium and rotation in WTTSs shows that: (1) rapidly rotating WTTSs have comparatively lower lithium abundances than their slower rotating counterparts; (2) in the spectral-type range G0-K0, most of the WTTSs share the same Li content irrespective of their Teff; and (3) active late-type binaries do not obey the correlation between lithium abundances and rotation periods, since the tidally locked rotation of the late-type binary system leads naturally to slower lithium destruction rates.
- ID:
- ivo://CDS.VizieR/J/MNRAS/472/334
- Title:
- Optical/MIR properties of Type 1 AGNs
- Short Name:
- J/MNRAS/472/334
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigated the connection between the mid-infrared (MIR) and optical spectral characteristics in a sample of 82 Type 1 active galactic nuclei (AGNs), observed with Infrared Spectrometer on Spitzer (IRS) and Sloan Digital Sky Survey (SDSS, DR12). We found several interesting correlations between optical and MIR spectral properties: (i) as starburst significators in MIR increase, the equivalent widths (EWs) of optical lines H{beta}NLR and FeII, increase as well; (ii) as MIR spectral index increases, EW([OIII]) decreases, while fractional contribution of AGN (RAGN) is not connected with EW([OIII]); (iii) The log([OIII]5007/H{beta}NLR) ratio is weakly related to the fractional contribution of polycyclic aromatic hydrocarbons (RPAHs). We compare the two different MIR and optical diagnostics for starburst contribution to the overall radiation (RPAH and Baldwin, Philips & Terlevich diagram, respectively). The significant differences between optical and MIR starburst diagnostics were found. The starburst influence to observed correlations between optical and MIR parameters is discussed.
- ID:
- ivo://CDS.VizieR/J/ApJS/183/261
- Title:
- Optical photometry of the ONC
- Short Name:
- J/ApJS/183/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present U, B, V, I broadband, 6200{AA} TiO medium band, and H{alpha} narrow band photometry of the Orion Nebula Cluster (ONC) obtained with the WFI imager at the ESO/MPI 2.2 telescope at La Silla Observatory. The nearly simultaneous observations cover the entire ONC in a field of about 34x34arcmin^2^. They enable us to determine stellar colors avoiding the additional scatter in the photometry induced by stellar variability typical of pre-main-sequence stars. We identify 2612 point-like sources in the I band; 58%, 43%, and 17% of them are also detected in V, B, and U, respectively. 1040 sources are identified in the H{alpha} band. In this paper we present the observations, the calibration techniques adopted, and the resulting catalog. We show the derived color-magnitude diagram of the population and discuss the completeness of our photometry. We define a spectrophotometric TiO index that takes into account the fluxes in the V, I, and TiO bands. Comparing it with spectral types of ONC members in the literature, we find a correlation between the index and the spectral type valid for M-type stars, which is accurate to better than 1 spectral subclass for M3-M6 types and better than 2 spectral subclasses for M0-M2 types. This allows us to newly classify 217 stars.
- ID:
- ivo://CDS.VizieR/J/ApJS/145/199
- Title:
- Optical spectroscopic atlas of low-redshift AGN
- Short Name:
- J/ApJS/145/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectral atlas of the H{beta} region for 215 type 1 AGNs (luminous Seyfert 1/radio galaxy nuclei and low-z quasars) up to z~0.8. Line profiles and measures were derived from the database of intermediate resolution spectra (R>~1000) with average continuum level S/N ratio ~30. Parameters including rest frame equivalent width and FWHM are provided for the FeII_opt_ blend at {lambda}4570, H{beta}, HeII {lambda}4686, and the [OIII] {lambda}{lambda}4959, 5007 emission lines. We extract clean broad component H{beta} profiles and provide wavelength measurements at 0, 1/4, 1/2, 3/4, and 0.9 peak intensity levels in order to permit a quantitative definition of the H{beta} broad component for statistical studies. We also discuss sources of uncertainty, selection effects, and biases in our sample. The data are especially important for tests of the eigenvector 1 parameter space occupation and correlation. We show that the I Zw 1 template FeII_opt_ spectrum reproduces well the observed FeII_opt_ emission for a wide range of line width and strength. A detailed analysis of the data within the eigenvector 1 context is deferred to a companion paper.
- ID:
- ivo://CDS.VizieR/J/ApJ/680/1295
- Title:
- Optical spectroscopy of Cha-II PMS stars
- Short Name:
- J/ApJ/680/1295
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss the results of the optical spectroscopic follow-up of pre-main-sequence (PMS) objects and candidates selected in the Chamaeleon II dark cloud based on data from the Spitzer Legacy survey "From Molecular Cores to Planet Forming Disks" (c2d) and from previous surveys. Our sample includes both objects with infrared excess selected according to c2d criteria and referred to as young stellar objects and other cloud members and candidates selected from complementary optical and near-infrared data. We characterize the sample of objects by deriving their physical parameters.
- ID:
- ivo://CDS.VizieR/J/AJ/130/1733
- Title:
- Optical spectroscopy of {rho} Oph stars
- Short Name:
- J/AJ/130/1733
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of optical spectroscopy of 139 stars obtained with the Hydra multiobject spectrograph. The objects extend over a 1.3{deg}^2^ area surrounding the main cloud of the {rho} Oph complex. The objects were selected from narrowband images to have H{alpha} in emission. Using the presence of strong H{alpha} emission, lithium absorption, location in the Hertzsprung-Russell diagram, or previously reported X-ray emission, we were able to identify 88 objects as young stars associated with the cloud. Strong H{alpha} emission was confirmed in 39 objects with line widths consistent with their origin in magnetospheric accretion columns. Two of the strongest emission-line objects are young, X-ray-emitting brown dwarf candidates with M8 spectral types. Comparisons of the bolometric luminosities and effective temperatures with theoretical models suggest a median age for this population of 2.1Myr, which is significantly older than the ages derived for objects in the cloud core. It appears that these stars formed contemporaneously with low-mass stars in the Upper Scorpius subgroup, likely triggered by massive stars in the Upper Centaurus subgroup.
