- ID:
- ivo://CDS.VizieR/J/ApJ/802/30
- Title:
- NGVS VI. Ultra-compact dwarfs in M87
- Short Name:
- J/ApJ/802/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The origin of ultra-compact dwarfs (UCDs; r_h_>~10pc) --objects larger and more massive than typical globular clusters (GCs), but more compact than typical dwarf galaxies-- has been hotly debated in the 15yrs since their discovery. Even whether UCDs should be considered galactic in origin, or simply the most extreme star clusters, is not yet settled. We present the dynamical properties of 97 spectroscopically confirmed UCDs and 911 GCs associated with the central cD galaxy of the Virgo cluster, M87. Our UCDs, of which 89% have M_*_>~2x10^6^M_{sun}_ and 92% are as blue as the classic blue GCs, nearly triple the confirmed sample of Virgo UCDs, providing by far the best opportunity for studying global dynamics of a UCD system. We found that (1) UCDs have a surface number density profile that is shallower than that of blue GCs in the inner ~70kpc and as steep as that of red GCs at larger radii; (2) UCDs exhibit a significantly stronger rotation than GCs, and blue GCs seem to have a velocity field that is more consistent with that of the surrounding dwarf ellipticals than with that of UCDs; (3) UCDs have an orbital anisotropy profile that is tangentially biased at radii <~40kpc and radially biased farther out, whereas blue GCs become more tangentially biased at larger radii beyond ~40kpc; (4) GCs with M_*_>~2x10^6^M_{sun}_ have rotational properties indistinguishable from the less massive ones, suggesting that it is the size, instead of mass, that differentiates UCDs from GCs as kinematically distinct populations. We conclude that most UCDs in M87 are not consistent with being merely the most luminous and extended examples of otherwise normal GCs. The radially biased orbital structure of UCDs at large radii is in general agreement with the "tidally threshed dwarf galaxy" scenario.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/143/149
- Title:
- NIR spectroscopy of Galactic Wolf-Rayet stars. II.
- Short Name:
- J/AJ/143/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We are continuing a J, K and narrowband imaging survey of 300{deg}^2^ of the plane of the Galaxy, searching for new Wolf-Rayet (W-R) stars. Our survey spans 150{deg} in Galactic longitude and reaches 1{deg} above and below the Galactic plane. The survey has a useful limiting magnitude of K=15 over most of the observed Galactic plane, and K=14 (due to severe crowding) within a few degrees of the Galactic center. Thousands of emission-line candidates have been detected. In spectrographic follow-ups of 146 relatively bright W-R star candidates, we have re-examined 11 previously known WC and WN stars and discovered 71 new W-R stars, 17 of type WN and 54 of type WC. Our latest image analysis pipeline now picks out W-R stars with a 57% success rate. Star subtype assignments have been confirmed with the K-band spectra and distances approximated using the method of spectroscopic parallax. Some of the new W-R stars are among the most distant known in our Galaxy. The distribution of these new W-R stars is beginning to trace the locations of massive stars along the distant spiral arms of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/2858
- Title:
- NIR spectroscopy of Galactic WR stars. III
- Short Name:
- J/MNRAS/452/2858
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new method of image subtraction is applied to images from a J, K, and narrow-band imaging survey of 300 deg2 of the plane of the Galaxy, searching for new Wolf-Rayet (WR) stars. Our survey spans 150{deg} in Galactic longitude and reaches b=+/-1{deg} with respect to the Galactic plane. The survey has a useful limiting magnitude of K=15 over most of the observed Galactic plane, and K=14 (due to severe crowding) within a few degrees of the Galactic Centre. The new image subtraction method described here (better than aperture or even point-spread-function photometry in very crowded fields) detected several thousand emission-line candidates. In 2011 and 2012 June and July, we spectroscopically followed up on 333 candidates with MDM-TIFKAM and Infrared Telescope Facility (IRTF)-SpeX, discovering 89 emission-line sources. These include 49 WR stars, 43 of them previously unidentified, including the most distant known Galactic WR stars, more than doubling the number on the far side of the Milky Way. We also demonstrate our survey's ability to detect very faint planetary nebulae and other NIR emission objects.
- ID:
- ivo://CDS.VizieR/J/ApJ/864/144
- Title:
- N/O and Ne/O ratios of SDSS dwarf galaxies
- Short Name:
- J/ApJ/864/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study how the void environment affects the chemical evolution of galaxies in the universe by comparing the oxygen and nitrogen abundances of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, we estimate the oxygen, nitrogen, and neon abundances of 889 void dwarf galaxies and 672 dwarf galaxies in denser regions. We use the Direct T_e_ method for calculating the gas-phase chemical abundances in the dwarf galaxies because it is best suited for low-metallicity, low-mass (dwarf) galaxies. A substitute for the [OII]{lambda}3727 doublet is developed, permitting oxygen abundance estimates of SDSS dwarf galaxies at all redshifts with the Direct T_e_ method. We find that void dwarf galaxies have about the same oxygen abundance and Ne/O ratio as dwarf galaxies in denser environments. However, we find that void dwarf galaxies have slightly higher neon (~10%) abundances than dwarf galaxies in denser environments. The opposite trend is seen in both the nitrogen abundance and N/O ratio: void dwarf galaxies have slightly lower nitrogen abundances (~5%) and lower N/O ratios (~7%) than dwarf galaxies in denser regions. Therefore, we conclude that the void environment has a slight influence on dwarf galaxy chemical evolution. Our mass-N/O relationship shows that the secondary production of nitrogen commences at a lower stellar mass in void dwarf star-forming galaxies than in dwarf star-forming galaxies in denser environments. We also find that star-forming void dwarf galaxies have higher HI masses than the star-forming dwarf galaxies in denser regions. Our star-forming dwarf galaxy sample demonstrates a strong anti-correlation between the sSFR and N/O ratio, providing evidence that oxygen is produced in higher-mass stars than those which synthesize nitrogen. The lower N/O ratios and smaller stellar mass for secondary nitrogen production seen in void dwarf galaxies may indicate both delayed star formation as predicted by {Lambda}CDM cosmology and a dependence of cosmic downsizing on the large-scale environment. A shift toward slightly higher oxygen abundances and higher HI masses in void dwarf galaxies could be evidence of larger ratios of dark matter halo mass to stellar mass in voids compared with denser regions.
- ID:
- ivo://CDS.VizieR/J/ApJS/239/26
- Title:
- NOFS astrometric measurements for distant WDs
- Short Name:
- J/ApJS/239/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station between 1989 and 2017, and the average uncertainty in the parallax values is 0.6mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric data set that spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for 19 stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a subsample of 179 white dwarfs (WDs) at distances of 25-200pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass, and cooling age of each WD. Twenty-six WDs are newly classified, and 12 systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of <8Gyr and masses close to the canonical 0.6M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/891/28
- Title:
- N-rich field stars from LAMOST and APOGEE data
- Short Name:
- J/ApJ/891/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interesting chemically peculiar field stars may reflect their stellar evolution history and their possible origin in a different environment from where they are found now; this is one of the most important research fields in Galactic archeology. To explore this further, we have used the CN-CH bands around 4000{AA} to identify N-rich metal-poor field stars in LAMOST DR3. Here we expand our N-rich, metal-poor field star sample to ~100 stars in LAMOST DR5, where 53 of them are newly found in this work. We investigate light elements of common stars between our sample and APOGEE DR14. While Mg, Al, and Si abundances generally agree with the hypothesis that N-rich metal-poor field stars come from enriched populations in globular clusters, it is still inconclusive for C, N, and O. After integrating the orbits of our N-rich field stars and a control sample of normal metal-poor field stars, we find that N-rich field stars have different orbital parameter distributions compared to the control sample-specifically, apocentric distances, maximum vertical amplitude (Zmax), orbital energy, and z-direction angular momentum (Lz). The orbital parameters of N-rich field stars indicate that most of them are inner-halo stars. The kinematics of N-rich field stars support their possible GC origin. The spatial and velocity distributions of our bona fide N-rich field star sample are important observational evidence to constrain simulations of the origin of these interesting objects.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/42
- Title:
- O and B type stars in W3: first results
- Short Name:
- J/ApJ/813/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from our survey of the star-forming complex W3, combining VRI photometry with multiobject spectroscopy to identify and characterize the high-mass stellar population across the region. With 79 new spectral classifications, we bring the total number of spectroscopically confirmed O- and B-type stars in W3 to 105. We find that the high-mass slope of the mass function in W3 is consistent with a Salpeter IMF, and that the extinction toward the region is best characterized by an R_V_ of approximately 3.6. B-type stars are found to be more widely dispersed across the W3 giant molecular cloud (GMC) than previously realized: they are not confined to the high-density layer (HDL) created by the expansion of the neighboring W4 H ii region into the GMC. This broader B-type population suggests that star formation in W3 began spontaneously up to 8-10 Myr ago, although at a lower level than the more recent star formation episodes in the HDL. In addition, we describe a method of optimizing sky subtraction for fiber spectra in regions of strong and spatially variable nebular emission.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A9
- Title:
- Obscured AGN at 1.5<z<3.0
- Short Name:
- J/A+A/626/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We select a sample of 90 obscured (type 2) AGN with 1.45<z<3.05 from the zCOSMOS-deep galaxy sample by 5 sigma-detection of the high-ionization CIV {lambda}1549 narrow emission line. The presence of this feature in a galaxy spectrum is often associated with nuclear activity, and the selection effectiveness has been also confirmed by ultraviolet (UV) emission line ratio diagnostic diagrams. Applying the same selection technique, a sample of 102 unobscured (type 1) AGN was collected. Taking advantage of the large amount of multi-band data available in the COSMOS field, we investigate the properties of the CIV-selected type 2 AGN, focusing on their host galaxies, X-ray emission and UV emission lines. Finally, we investigate the physical properties of the ionized gas in the Narrow Line Region (NLR) of this type 2 AGN sample, combining the analysis of strong UV emission lines with predictions from photo-ionization models. We find that, in order to successfully reproduce the relative intensity of UV emission lines of the selected high-z type 2 AGN, two new ingredients in the photo-ionization models are fundamental,i.e. small inner radii of the NLR (~90pc for LAGN=10^45^erg/s) and the internal dissipative micro-turbulence of the gas emitting clouds (with v_micr_~100km/s). With these modified models, we compute the gas-phase metallicity of the NLR, and our measurements indicate a statistically significant evolution of the metal content with redshift. Finally, we do not observe, in our CIV-selected type 2 AGN sample, a strong relationship between the NLR gas metallicity and the stellar mass of the host galaxy.
- ID:
- ivo://CDS.VizieR/J/AJ/159/255
- Title:
- Observation & radial velocity of WASP-150 & WASP-176
- Short Name:
- J/AJ/159/255
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of two transiting exoplanets from the Wide Angle Search for Planets (WASP) survey, WASP-150b and WASP-176b. WASP-150b is an eccentric (e=0.38) hot Jupiter on a 5.6day orbit around a V=12.03, F8 main-sequence host. The host star has a mass and radius of 1.4M_{sun}_ and 1.7R_{sun}_ respectively. WASP-150b has a mass and radius of 8.5M_J_ and 1.1R_J_, leading to a large planetary bulk density of 6.4{rho}_J_. WASP-150b is found to be ~3Gyr old, well below its circularization timescale, supporting the eccentric nature of the planet. WASP-176b is a hot Jupiter planet on a 3.9day orbit around a V=12.01, F9 sub-giant host. The host star has a mass and radius of 1.3M{sun} and 1.9R{sun}. WASP-176b has a mass and radius of 0.86M_J_ and 1.5R_J_, respectively, leading to a planetary bulk density of 0.23{rho}_J_.
- ID:
- ivo://CDS.VizieR/J/AJ/159/233
- Title:
- Observations of binary stars with the DSSI. IX.
- Short Name:
- J/AJ/159/233
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report 370 measures of 170 components of binary and multiple-star systems, obtained from speckle imaging observations made with the Differential Speckle Survey Instrument (DSSI) at Lowell Observatory's Discovery Channel Telescope in 2015 through 2017. Of the systems studied, 147 are binary stars, 10 are seen as triple systems, and 1 quadruple system is measured. Seventy-six high-quality nondetections and 15 newly resolved components are presented in our observations. The uncertainty in relative astrometry appears to be similar to our previous work at Lowell, namely, linear measurement uncertainties of approximately 2mas, and the relative photometry appears to be uncertain at the 0.1-0.15mag level. Using these measures and those in the literature, we calculate six new visual orbits, including one for the Be star 66Oph and two combined spectroscopic-visual orbits. The latter two orbits, which are for HD22451 (YSC127) and HD185501 (YSC135), yield individual masses of the components at the level of 2% or better, and independent distance measures that in one case agrees with the value found in the Gaia DR2 and in the other disagrees at the 2{sigma} level. We find that HD22451 consists of an F6V+F7V pair with orbital period of 2401.1{+/-}3.2days and masses of 1.342{+/-}0.029 and 1.236{+/-}0.026M_{sun}_. For HD185501, both stars are G5 dwarfs that orbit one another with a period of 433.94{+/-}0.15days, and the masses are 0.898{+/-}0.012 and 0.876{+/-}0.012M_{sun}_. We discuss the details of both the new discoveries and the orbit objects.