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551. Cygnus OB2 O stars spectroscopic analysis
ID:
ivo://CDS.VizieR/J/A+A/642/A168
Title:
Cygnus OB2 O stars spectroscopic analysis
Short Name:
J/A+A/642/A168
Date:
21 Oct 2021
Publisher:
CDS
Description:
Cygnus OB2 provides a unique insight into the high-mass stellar content in one of the largest groups of young massive stars in our Galaxy. Although several studies of its massive population have been carried out over the last decades, an extensive spectroscopic study of the whole known O-star population in the association is still lacking. In this work, we created the most complete spectroscopic census of O stars carried out so far in Cygnus OB2 using already existing and new spectroscopy. We present the spectra for 78 O-type stars, from which we identify new binary systems, obtain the distribution of rotational velocities, and determine the main stellar parameters for all the stars in the region that have not been detected as double-line spectroscopic binaries. We also derive radii, luminosities, and masses for those stars with reliable Gaia astrometry, in addition to creating the Hertzsprung- Russell Diagram to interpret the evolutionary status of the association. This work has shown the improvement reached when using accurate spectroscopic parameters and astrometry for the interpretation of the evolutionary status of a population, revealing, in the case of Cygnus OB2, at least two star-forming bursts at ~3 and ~5Myr. We find an apparent deficit of very fast rotators in the distribution of rotational velocities. The inspection of the dynamical distribution of the sample has allowed us to identify nine O stars with peculiar proper motions and discuss a possible dynamical ejection scenario or past supernova explosions in the region.
552. Cygnus X-3 IR spectra
ID:
ivo://CDS.VizieR/J/MNRAS/308/473
Title:
Cygnus X-3 IR spectra
Short Name:
J/MNRAS/308/473
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present four epochs, A, B, C and D, of resolution ({lambda}/{delta}{lambda}) = 1200, 2.12 micron spectroscopy of the peculiar X-ray binary Cygnus X-3. About a half dozen spectra taken with resolution 900, and at 1.62 micron are also included. These data were obtained using the FSpec near-infrared spectrometer (Williams, D., Thompson, C.L., Rieke, G.H., Montgomery, E. 1993, Proc. SPIE 1308, 482) on the Multiple Mirror Telescope (MMT). The MMT is located at an elevation of 2600 m at the top of Mt. Hopkins in southern Arizona and is jointly operated by the Smithsonian Astrophysics Observatory and the University of Arizona. The spectra are stored as ascii files, listing wavelength in Angstroms and relative flux. Each file contains a five line header, giving the UT, Heliocentric Julian date and phase of the X-ray system at the start of the integration, followed by the data points. Additional information about the spectra can be obtained in the paper.
553. CzeV404 Her light curves and spectra
ID:
ivo://CDS.VizieR/J/A+A/652/A49
Title:
CzeV404 Her light curves and spectra
Short Name:
J/A+A/652/A49
Date:
22 Feb 2022
Publisher:
CDS
Description:
We present a new study of the eclipsing cataclysmic variable CzeV404 Her (Porb=0.098d) located in the period gap. This report aims to determine the object's origin, system parameters and probe the system's accretion flow structure. We conducted simultaneous time-resolved photometric and spectroscopic observations of CzeV404 Her. We applied our light curve modeling techniques and the Doppler tomography method to determine the system parameters and analyse the structure of the accretion disk. We found that the system has a massive white dwarf M_WD_=1.00(2)M_{sun}_, a mass ratio of q=0.16, and a relatively hot secondary with an effective temperature T_2_=4100(50)K. The system inclination is 78{deg}. The accretion disk spreads out to the tidal limitation radius and has an extended hot spot/line region. The hot spot/line is hotter than the rest of the disk's outer part in quiescence or intermediate state but does not stand out completely from the disk flux in (super)outbursts. We claim that this object represents a link between two distinct classes of SU UMa-type and SW Sex-type cataclysmic variables. The accretion flow structure in the disk corresponds to the SW Sex systems, but the physical conditions inside the disk passed into behaviors of SU UMa-type objects.
554. Damped Lyman{alpha} absorbers in z>4 QSOs
ID:
ivo://CDS.VizieR/J/A+A/508/133
Title:
Damped Lyman{alpha} absorbers in z>4 QSOs
Short Name:
J/A+A/508/133
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a survey of damped (DLA, logN(HI)>20.3) and sub-damped Lyman-{alpha} systems (19.5<logN(HI)<20.3) at z>2.55 along the lines-of-sight to 77 quasars with emission redshifts in the range 4<z_em_<6.3. Intermediate resolution (R~4300) spectra were obtained with the Echellette Spectrograph and Imager (ESI) mounted on the Keck telescope. A total of 100 systems with logN(HI)>19.5 were detected of which 40 systems are damped Lyman-{alpha} systems for an absorption length of {Delta}X= 378. About half of the lines of sight of this homogeneous survey have never been investigated for DLAs.
555. Dark dust and single-cloud sightlines in ISM
ID:
ivo://CDS.VizieR/J/A+A/641/A35
Title:
Dark dust and single-cloud sightlines in ISM
Short Name:
J/A+A/641/A35
Date:
21 Oct 2021
Publisher:
CDS
Description:
The precise characteristics of clouds and the nature of dust in the diffuse interstellar medium can only be extracted by inspecting the rare cases of single-cloud sightlines. In our nomenclature such objects are identified by interstellar lines, such as KI, that show at a resolving power of {lambda}{Delta}{lambda}~75000 one dominating Doppler component that accounts for more than half of the observed column density. We searched for such sightlines using high-resolution spectroscopy towards reddened OB stars for which far-UV extinction curves are known. We compiled a sample of 186 spectra, 100 of which were obtained specifically for this project with UVES. In our sample we identified 65 single-cloud sightlines, about half of which were previously unknown. We used the CH/CH^+^ line ratio of our targets to establish whether the sightlines are dominated by warm or cold clouds. We found that CN is detected in all cold (CH/CH^+^>1) clouds, but {is frequently absent} in warm clouds. We inspected the WISE (3-22um) observed emission morphology around our sightlines and excluded a circumstellar nature for the observed dust extinction. We found that most sightlines are dominated by cold clouds that are located far away from the heating source. For 132 stars, we derived the spectral type and the associated spectral type-luminosity distance. We also applied the interstellar CaII distance scale, and compared these two distance estimates with GAIA parallaxes. These distance estimates scatter by ~40%. By comparing spectral type-luminosity distances with those of GAIA, we detected a hidden dust component that amounts to a few mag of extinction for eight sightlines. This dark dust is populated by >~ 1um large grains and predominately appears in the field of the cold interstellar medium.
556. 500days of ASASSN-18pg multiwavelength obs.
ID:
ivo://CDS.VizieR/J/ApJ/898/161
Title:
500days of ASASSN-18pg multiwavelength obs.
Short Name:
J/ApJ/898/161
Date:
16 Mar 2022 00:55:51
Publisher:
CDS
Description:
We present nearly 500 days of observations of the tidal disruption event (TDE) ASASSN-18pg, spanning from 54 days before peak light to 441 days after peak light. Our data set includes X-ray, UV, and optical photometry, optical spectroscopy, radio observations, and the first published spectropolarimetric observations of a TDE. ASASSN-18pg was discovered on 2018 July 11 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d=78.6Mpc; with a peak UV magnitude of m~14, it is both one of the nearest and brightest TDEs discovered to-date. The photometric data allow us to track both the rise to peak and the long-term evolution of the TDE. ASASSN-18pg peaked at a luminosity of L~2.4x10^44^erg/s, and its late-time evolution is shallower than a flux {propto}t^-5/3^ power-law model, similar to what has been seen in other TDEs. ASASSN-18pg exhibited Balmer lines and spectroscopic features consistent with Bowen fluorescence prior to peak, which remained detectable for roughly 225days after peak. Analysis of the two-component H{alpha} profile indicates that, if they are the result of reprocessing of emission from the accretion disk, the different spectroscopic lines may be coming from regions between ~10 and ~60 lt-days from the black hole. No X-ray emission is detected from the TDE, and there is no evidence of a jet or strong outflow detected in the radio. Our spectropolarimetric observations indicate that the projected emission region is likely not significantly aspherical, with the projected emission region having an axis ratio of >~0.65.
557. DB white dwarfs from the Hamburg/ESO survey
ID:
ivo://CDS.VizieR/J/A+A/363/1040
Title:
DB white dwarfs from the Hamburg/ESO survey
Short Name:
J/A+A/363/1040
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an analysis of 40 cool helium-rich white dwarfs found in the Hamburg/ESO survey. They were selected for follow-up spectroscopy because of their U-B colour below -0.18, the absence of strong absorption lines, and a continuum shape similar to that of a quasar. Effective temperatures for individual stars were determined by fitting model atmospheres of nearly pure helium with a small admixture of hydrogen. As a consequence of the selection criteria all but one sample stars have T_eff_ below 20000K. Four stars clearly show helium and hydrogen lines in their spectra. In the spectra of another three, helium, hydrogen, and metal lines can be detected. For these stars hydrogen and metal abundances were also determined by fitting appropriate model atmospheres containing these elements. Seven sample stars most likely have helium-rich atmospheres but do not show any helium lines. They either have featureless spectra or show calcium lines.
558. DB white dwarfs with SDSS and Gaia data
ID:
ivo://CDS.VizieR/J/ApJ/882/106
Title:
DB white dwarfs with SDSS and Gaia data
Short Name:
J/ApJ/882/106
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comprehensive analysis of DB white dwarfs drawn from the Sloan Digital Sky Survey, based on model fits to ugriz photometry and medium-resolution spectroscopy from the Sloan Digital Sky Survey. We also take advantage of the exquisite trigonometric parallax measurements recently obtained by the Gaia mission. Using the so-called photometric and spectroscopic techniques, we measure the atmospheric and physical parameters of each object in our sample (Teff, logg, H/He, Ca/He, R, M), and compare the values obtained from both techniques in order to assess the precision and accuracy of each method. We then explore in great detail the surface gravity, stellar mass, and hydrogen abundance distributions of DB white dwarfs as a function of effective temperature. We present some clear evidence for a large population of unresolved double-degenerate binaries composed of DB+DB and even DB+DA white dwarfs. In the light of our results, we finally discuss the spectral evolution of DB white dwarfs, in particular the evolution of the DB-to-DA ratio as a function of Teff, and we revisit the question of the origin of hydrogen in DBA white dwarfs.
559. Debris disks in NGC 2232
ID:
ivo://CDS.VizieR/J/ApJ/688/597
Title:
Debris disks in NGC 2232
Short Name:
J/ApJ/688/597
Date:
21 Oct 2021
Publisher:
CDS
Description:
We describe Spitzer IRAC and MIPS observations of the nearby 25Myr old open cluster NGC 2232. Combining these data with ROSAT All-Sky Survey observations, proper motions, and optical photometry/spectroscopy, we construct a list of highly probable cluster members. We identify one A-type star, HD 45435, that has definite excess emission at 4.5-24um indicative of debris from terrestrial planet formation. We also identify 2-4 late-type stars with possible 8um excesses and 8 early-type stars with definite 24um excesses. Constraints on the dust luminosity and temperature suggest that the detected excesses are produced by debris disks. From our sample of B and A stars, stellar rotation appears to be correlated with 24um excess, a result that would be expected if massive primordial disks evolve into massive debris disks. To explore the evolution of the frequency and magnitude of debris around A-type stars, we combine our results with data for other young clusters.
560. Deep echelle spectrophotometry of NGC3918
ID:
ivo://CDS.VizieR/J/MNRAS/452/2606
Title:
Deep echelle spectrophotometry of NGC3918
Short Name:
J/MNRAS/452/2606
Date:
21 Oct 2021
Publisher:
CDS
Description:
The chemical content of the planetary nebula NGC 3918 is investigated through deep, high-resolution (R~40000) UVES (Ultraviolet-Visual Echelle Spectrograph) at VLT (Very Large Telescope) spectrophotometric data. We identify and measure more than 750 emission lines, making ours one of the deepest spectra ever taken for a planetary nebula. Among these lines we detect very faint lines of several neutron-capture elements (Se, Kr, Rb, and Xe), which enable us to compute their chemical abundances with unprecedented accuracy, thus constraining the efficiency of the s-process and convective dredge-up in NGC 3918 progenitor star. We find that Kr is strongly enriched in NGC 3918 and that Se is less enriched than Kr, in agreement with the results of previous papers and with predicted s-process nucleosynthesis. We also find that Xe is not as enriched by the s-process in NGC 3918 as is Kr and, therefore, that neutron exposure is typical of modestly subsolar metallicity asymptotic giant branch (AGB) stars. A clear correlation is found when representing [Kr/O] versus log(C/O) for NGC 3918 and other objects with detection of multiple ions of Kr in optical data, confirming that carbon is brought to the surface of AGB stars along with s-processed material during third dredge-up episodes, as predicted by nucleosynthesis models. We also detect numerous refractory element lines (Ca, K, Cr, Mn, Fe, Co, Ni, and Cu) and a large number of metal recombination lines of C, N, O, and Ne. We compute physical conditions from a large number of diagnostics, which are highly consistent among themselves assuming a three-zone ionization scheme. Thanks to the high ionization of NGC 3918 we detect a large number of recombination lines of multiple ionization stages of C, N, O and Ne. The abundances obtained for these elements by using recently determined state-of-the-art ionization correction factor (ICF) schemes or simply adding ionic abundances are in very good agreement, demonstrating the quality of the recent ICF scheme for high-ionization planetary nebulae.

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