- ID:
- ivo://CDS.VizieR/J/AJ/153/128
- Title:
- WOCS. LXXV. Hyades&Praesepe stellar lithium data
- Short Name:
- J/AJ/153/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- WIYN/Hydra spectroscopy (at R~15000) of the moderately metal-rich Praesepe and Hyades open clusters was used to study their main-sequence (MS) iron ([Fe/H]) and lithium (A(Li)) abundances. Self-consistent [Fe/H] and Li analyses of these clusters of consistent age, which we re-evaluate, confirms that they have consistent [Fe/H] and provides a foundation to investigate the poorly understood G-dwarf and F-dwarf Li-depletions. Neither phenomenon agrees with standard stellar evolution theory, but possible explanations abound. We supplement our A(Li) with previously published results placed on a uniform abundance scale. This creates the largest self-consistently analyzed sample of A(Li) in both the Hyades (90) and Praesepe (110). For each star, high-precision UBVRI photometry was used to determine a 10-color-based T_eff_ and then to test for photometric peculiarities indicated by a large {sigma}_Teff_ (>75 K). The stars that have large {sigma}_Teff_ were predominantly found to be binaries or stars with peculiar (apparent) A(Li). When considering only proper-motion members that have low {sigma}_Teff_ and are also photometrically consistent with the cluster MS fiducial, each cluster has a more tightly defined Li morphology than previously observed and the two clusters' A(Li) are indistinguishable. This suggests that clusters of consistent age and metallicity may have consistent Li-depletion trends across a broad range of T_eff_; no additional major parameters are required, at least for these two clusters. We propose that the combined Hyades and Praesepe data offer more rigorous constraints than does either cluster alone, and we discuss newly revealed features of the combined Li-T_eff_ trend.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/454/1525
- Title:
- XMM-Newton and Chandra monitoring of Sgr A*
- Short Name:
- J/MNRAS/454/1525
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the X-ray flaring activity of Sgr A* during all the 150 XMM-Newton and Chandra observations pointed at the Milky Way centre over the last 15 years. This includes the latest XMM-Newton and Chandra campaigns devoted to monitoring the closest approach of the very red Br{gamma} emitting object called G2. The entire data set analysed extends from 1999 September through 2014 November. We employed a Bayesian block analysis to investigate any possible variations in the characteristics (frequency, energetics, peak intensity, duration) of the flaring events that Sgr A* has exhibited since their discovery in 2001. We observe that the total bright or very bright flare luminosity of Sgr A* increased between 2013 and 2014 by a factor of 2-3 (~3.5{sigma} significance). We also observe an increase (~99.9 percent significance) from 0.27+/-0.04 to 2.5+/-1.0/d of the bright or very bright flaring rate of Sgr A*, starting in late summer 2014, which happens to be about six months after G2's pericentre passage. This might indicate that clustering is a general property of bright flares and that it is associated with a stationary noise process producing flares not uniformly distributed in time (similar to what is observed in other quiescent black holes). If so, the variation in flaring properties would be revealed only now because of the increased monitoring frequency. Alternatively, this may be the first sign of an excess accretion activity induced by the close passage of G2. More observations are necessary to distinguish between these two hypotheses.
- ID:
- ivo://CDS.VizieR/J/MNRAS/351/31
- Title:
- XMM-Newton Galactic Plane Survey (XGPS)
- Short Name:
- J/MNRAS/351/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from the XMM-Newton Galactic Plane Survey (XGPS). In the first phase of the programme, 22 pointings were used to cover a region of approximately 3 deg^2^between 19{deg} and 22{deg} in Galactic longitude and +/-0.6{deg} in latitude. In total we have resolved over 400 point X-ray sources, at >=5{sigma} significance, down to a flux limit of ~2x10^-14^erg/s/cm^2^(2-10 keV).
- ID:
- ivo://CDS.VizieR/J/AJ/157/176
- Title:
- X-ray emission from Galactic stellar bow shocks
- Short Name:
- J/AJ/157/176
- Date:
- 03 Nov 2021 07:20:14
- Publisher:
- CDS
- Description:
- We present a stacking analysis of 2.61 Ms of archival Chandra observations of stellar wind bow shocks. We place an upper limit on the X-ray luminosity of infrared-detected bow shocks of <2x10^29^ erg/s, a more stringent constraint than has been found in previous archival studies and dedicated observing campaigns of nearby bow shocks. We compare the X-ray luminosities and L_X_/L_bol_ ratios of bow shock driving stars to those of other OB stars within the Chandra field of view. Driving stars are, on average, of later spectral type than the field-of-view OB stars, and we do not observe any unambiguously high L_X_/L_bol_ ratios indicative of magnetic stars in our sample. We additionally assess the feasibility of detecting X-rays from stellar wind bow shocks with the proposed Lynx X-ray Observatory. If the X-ray flux originating from the bow shocks is just below our Chandra detection limit, the nearest bow shock in our sample (at ~0.4 kpc with an absorbing column of ~10^21^/cm^2^) should be observable with Lynx in exposure times on the order of ~100 ks.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/34
- Title:
- X-ray spectral analysis of 107 MW sight lines
- Short Name:
- J/ApJ/862/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation mechanism of the hot gaseous halo associated with the Milky Way is still under debate. We report new observational constraints on the gaseous halo using 107 lines of sight of the Suzaku X-ray observations at 75{deg}<l<285{deg} and |b|>15{deg} with a total exposure of 6.4Ms. The gaseous halo spectra are represented by a single-temperature plasma model in collisional ionization equilibrium. The median temperature of the observed fields is 0.26keV (3.0x10^6^K) with a typical fluctuation of ~30%. The emission measure varies by an order of magnitude and marginally correlates with the Galactic latitude. Despite the large scatter of the data, the emission measure distribution is roughly reproduced by a disk-like density distribution with a scale length of ~7kpc, a scale height of ~2kpc, and a total mass of ~5x10^7^M_{sun}_. In addition, we found that a spherical hot gas with the {beta}-model profile hardly contributes to the observed X-rays but that its total mass might reach >~10^9^M_{sun}_. Combined with indirect evidence of an extended gaseous halo from other observations, the hot gaseous halo likely consists of a dense disk-like component and a rarefied spherical component; the X-ray emissions primarily come from the former, but the mass is dominated by the latter. The disk-like component likely originates from stellar feedback in the Galactic disk due to the low scale height and the large scatter of the emission measures. The median [O/Fe] of ~0.25 shows the contribution of the core-collapse supernovae and supports the stellar feedback origin.
- ID:
- ivo://CDS.VizieR/J/ApJ/788/105
- Title:
- XSTPS RR Lyrae in the north Galactic cap
- Short Name:
- J/ApJ/788/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XSTPS). The area we consider is located in the north Galactic cap, covering ~376.75 deg^2^ at RA~150{deg} and DE~27{deg} down to a magnitude limit of i~19. Using the variability information afforded by the multi-epoch nature of our XSTPS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them, and estimate the detection efficiency. The majority of our candidates have more than 12 observations, and for these we are able to calculate periods. These also allow us to estimate our contamination level, which we predict is between 30% and 40%. Finally, we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the south Galactic cap using the Watkins et al. (2009, J/MNRAS/398/1757) and Sesar et al. (2010, J/ApJ/708/717) RRL data sets, after accounting for possible contamination in our data set from Sagittarius stream members. We consider non-spherical double power-law models of the halo density profile and again find agreement with literature data sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material; as an example the first few entries of each electronic table are shown in the text.
- ID:
- ivo://CDS.VizieR/J/ApJ/799/153
- Title:
- Yellowballs in Milky Way project
- Short Name:
- J/ApJ/799/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Yellowballs are a collection of approximately 900 compact, infrared sources identified and named by volunteers participating in the Milky Way Project (MWP), a citizen science project that uses GLIMPSE/MIPSGAL images from Spitzer to explore topics related to Galactic star formation. In this paper, through a combination of catalog cross-matching and infrared color analysis, we show that yellowballs are a mix of compact star-forming regions, including ultra-compact and compact HII regions, as well as analogous regions for less massive B-type stars. The resulting MWP yellowball catalog provides a useful complement to the Red MSX Source survey. It similarly highlights regions of massive star formation, but the selection of objects purely on the basis of their infrared morphology and color in Spitzer images identifies a signature of compact star-forming regions shared across a broad range of luminosities and, by inference, masses. We discuss the origin of their striking mid-infrared appearance and suggest that future studies of the yellowball sample will improve our understanding of how massive and intermediate-mass star-forming regions transition from compact to more extended bubble-like structures.
- ID:
- ivo://CDS.VizieR/J/AJ/158/201
- Title:
- Young star cluster Westerlund 2 observed with MUSE
- Short Name:
- J/AJ/158/201
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We mapped the Galactic young massive star cluster Westerlund 2 with the integral field spectrograph MUSE (spatial resolution: 0.2 arcsec/px, spectral resolution: {Delta}{lambda}=1.25 {AA}, wavelength range: 4600-9350 {AA}) mounted on the Very Large Telescope. We present the fully reduced data set and introduce our new Python package "MUSEpack", which we developed to measure stellar radial velocities (RVs) with an absolute precision of 1-2 km/s without the necessity of a spectral template library. This novel method uses the two-dimensional spectra and an atomic transition line library to create templates around strong absorption lines for each individual star. Automatic, multi-core processing makes it possible to efficiently determine stellar RVs of a large number of stars with the necessary precision to measure the velocity dispersion of young star clusters. MUSEpack also provides an enhanced method for removing telluric lines in crowded fields without sky exposures, and a Python wrapper for ESO's data reduction pipeline. We observed Westerlund 2 with a total of 11 short and 5 long exposures (survey area: ~11 arcmin^2^ or 15.8 pc^2^) to cover the bright nebular emission and OB stars, as well as the fainter pre-main-sequence stars (>=1 M_{sun}_). We extracted 1725 stellar spectra with a mean signal-to-noise ratio of S/N>5 per pixel. Typical RV uncertainties of 4.78 km/s, 2.92 km/s, and 1.1 km/s are reached for stars with a mean S/N>10, S/N>20, and S/N>50 per pixel, respectively. It is possible to reach RV accuracies of 0.9 km/s, 1.3 km/s, and 2.2 km/s with >=5, 3-4, and 1-2 spectral lines used to measure the RVs, respectively. The combined statistical uncertainty on the RV measurements is 1.10 km/s.
- ID:
- ivo://CDS.VizieR/J/ApJS/223/15
- Title:
- 8yr INTEGRAL/IBIS soft gamma-ray source obs.
- Short Name:
- J/ApJS/223/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Here we report an all-sky soft gamma-ray source catalog based on IBIS observations performed during the first 1000 orbits of INTEGRAL. The database for the construction of the source list consists of all good-quality data available, from the launch in 2002, up to the end of 2010. This corresponds to ~110Ms of scientific public observations, with a concentrated coverage on the Galactic Plane and extragalactic deep exposures. This new catalog includes 939 sources above a 4.5{sigma} significance threshold detected in the 17-100keV energy band, of which 120 sources represent previously undiscovered soft gamma-ray emitters. The source positions are determined, mean fluxes are provided in two main energy bands, and these are both reported together with the overall source exposure. Indicative levels of variability are provided, and outburst times and durations are given for transient sources. A comparison is made with previous IBIS catalogs and catalogs from other similar missions.
- ID:
- ivo://CDS.VizieR/J/ApJ/820/90
- Title:
- 4yr 1.3mm VLBI observations of SgrA* with EHT
- Short Name:
- J/ApJ/820/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3mm emission from this source on angular scales comparable to that of the general relativistic shadow. Previous EHT observations have used visibility amplitudes to infer the morphology of the millimeter-wavelength emission. Potentially much richer source information is contained in the phases. We report on 1.3mm phase information on Sgr A* obtained with the EHT on a total of 13 observing nights over four years. Closure phases, which are the sum of visibility phases along a closed triangle of interferometer baselines, are used because they are robust against phase corruptions introduced by instrumentation and the rapidly variable atmosphere. The median closure phase on a triangle including telescopes in California, Hawaii, and Arizona is nonzero. This result conclusively demonstrates that the millimeter emission is asymmetric on scales of a few Schwarzschild radii and can be used to break 180{deg} rotational ambiguities inherent from amplitude data alone. The stability of the sign of the closure phase over most observing nights indicates persistent asymmetry in the image of Sgr A* that is not obscured by refraction due to interstellar electrons along the line of sight.
