Search

Start Over Subject optical astronomy Capability Type Simple Cone Search
1811. NTT, HDF-S and HDF-N photometric redshifts
ID:
ivo://CDS.VizieR/J/AJ/120/2206
Title:
NTT, HDF-S and HDF-N photometric redshifts
Short Name:
J/AJ/120/2206
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present and compare in this paper new photometric redshift catalogs of the galaxies in three public fields: the NTT Deep Field, the HDF-N, and the HDF-S. In the case of the NTT Deep Field, we present here a new photometric catalog, obtained by combining the existing BVrI and JKs with new deep U observations acquired with NTT-SUSI2, and which includes also the contiguous field centered on the z_em_=4.7 quasar BR 1202-0
1812. NuSTAR Extragalactic Surveys, NEP Field
ID:
ivo://CDS.VizieR/J/MNRAS/508/5176
Title:
NuSTAR Extragalactic Surveys, NEP Field
Short Name:
J/MNRAS/508/5176
Date:
03 Dec 2021 13:27:09
Publisher:
CDS
Description:
We present the NuSTAR extragalactic survey of the James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field. The survey covers a ~0.16deg^2^ area with a total exposure of 681ks acquired in a total of nine observations from three epochs. The survey sensitivities at 20% of the area are 2.39, 1.14, 2.76, 1.52, and 5.20x10^-14^erg/cm^2^/s in the 3-24, 3-8, 8-24, 8-16, and 16-24keV bands, respectively. The NEP survey is one of the most sensitive extragalactic surveys with NuSTAR so far. A total of 33 sources were detected above 95% reliability in at least one of the five bands. We present the number counts, logN-logS, measured in the hard X-ray 8-24 and 8-16keV bands, uniquely accessible by NuSTAR down to such faint fluxes. We performed source detection on the XMM-Newton and Chandra observations of the same field to search for soft X-ray counterparts of each NuSTAR detection. The soft band positions were used to identify optical and infrared associations. We present the X-ray properties (hardness ratio and luminosity) and optical-to-X-ray properties of the detected sources. The measured fraction of candidate Compton-thick (NH>=10^24^cm^-2^) active galactic nuclei, derived from the hardness ratio, is between 3% to 27%. As this survey was designed to have variability as its primary focus, we present preliminary results on multi-epoch flux variability in the 3-24keV band.
1813. NuSTAR Extragalactic Surveys: UDS field
ID:
ivo://CDS.VizieR/J/ApJS/235/17
Title:
NuSTAR Extragalactic Surveys: UDS field
Short Name:
J/ApJS/235/17
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results and the source catalog of the NuSTAR survey in the UKIDSS Ultra Deep Survey (UDS) field, bridging the gap in depth and area between NuSTAR's ECDFS and COSMOS surveys. The survey covers a ~0.6deg^2^ area of the field for a total observing time of ~1.75Ms, to a half-area depth of ~155ks corrected for vignetting at 3-24keV, and reaching sensitivity limits at half-area in the full (3-24keV), soft (3-8keV), and hard (8-24keV) bands of 2.2x10^-14^erg/cm^2^/s, 1.0x10^-14^erg/cm^2^/s, and 2.7x10^-14^erg/cm^2^/s, respectively. A total of 67 sources are detected in at least one of the three bands, 56 of which have a robust optical redshift with a median of <z>~1.1. Through a broadband (0.5-24keV) spectral analysis of the whole sample combined with the NuSTAR hardness ratios, we compute the observed Compton-thick (CT; N_H_>10^24^cm^-2^) fraction. Taking into account the uncertainties on each NH measurement, the final number of CT sources is 6.8+/-1.2. This corresponds to an observed CT fraction of 11.5%+/-2.0%, providing a robust lower limit to the intrinsic fraction of CT active galactic nuclei and placing constraints on cosmic X-ray background synthesis models.
1814. NVSS and FIRST variable sources
ID:
ivo://CDS.VizieR/J/other/A+C/25.176
Title:
NVSS and FIRST variable sources
Short Name:
J/other/A+C/25.1
Date:
21 Oct 2021
Publisher:
CDS
Description:
In the present study we have cross-correlated NVSS and FIRST radio catalogues having radio flux measurements at the same 1.4GHz frequency. This way we benefit from repeated observations from both catalogues, as they give more accurate positions and fluxes and more important, reveal large differences between the two measured fluxes, thus allowing to establish radio variability. As a result 79382 radio variables have been revealed, including 6301 with flux differences at 1.4GHz larger than 15mJy, 1917 with flux differences 45mJy and 260 with flux differences 200mJy. By using a special technique (Mickaelian & Sinamyan 2010 (J/MNRAS/407/681) Mickaelian+ 2011 (J/MNRAS/415/1061)), 2425 optically variable objects out of 6301 radio sources have been revealed. 2425 radio sources with both high radio and optical variability into four categories have been divided. 1206 (19%) out of 6301 radio sources have activity types from available catalogues and 619 (25.5%) out of 2425 radio sources with at the same time radio and optical variability have activity types from available catalogues. In addition, 279 radio sources out of 2425 have high variability in optical range. We have established their activity types when available. The IR fluxes and colours for the 6301 variable radio sources have been studied. Colour-colour diagrams show that most of the "unknown" sources are galaxies. The activity types for 110 (42%) out of 260 extremely high variable radio sources also have been retrieved.
1815. O and B type stars in W3: first results
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.
1816. OB Associations and Spiral Structure in M33
ID:
ivo://CDS.VizieR/J/AJ/105/499
Title:
OB Associations and Spiral Structure in M33
Short Name:
J/AJ/105/499
Date:
21 Oct 2021
Publisher:
CDS
Description:
This file contains UBV photometry for the brightest stars in the southern spiral arm of M33. All stars brighter than V=21 are included in this file. For details on the observations and data reduction see reference. All the data is in ASCII format of the file. The observations where carried out on the Palomar 60in. telescope.
1817. OB Associations of the Northern Milky Way
ID:
ivo://CDS.VizieR/J/ApJ/454/151
Title:
OB Associations of the Northern Milky Way
Short Name:
J/ApJ/454/151
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the massive star content of Milky Way clusters and OB associations in order to answer three questions: (1) How coeval is star formation? (2) How constant is the initial mass function (IMF)? (3) What is the progenitor mass of Wolf-Rayet stars? Our sample includes NGC 6823/Vul OB1, NGC 6871/Cyg OB3, Berkeley 86/Cyg OB1, NGC 6913/Cyg OB1, NGC 7235, NGC 7380/Cep OB1, Cep OB5, IC 1805/Cas OB6, NGC 1893/Aur OB2, and NGC 2244/Mon OB2. Large-field CCD imaging and multiobject, fiber spectroscopy has resulted in UBV photometry for >10,000 stars and new spectral types for ~200 stars. These data are used to redetermine distances and reddenings for these regions and to help exclude probable nonmembers in constructing the H-R diagrams. We reanalyze comparable data previously published on Cyg OB2, Tr 14/16, and NGC 6611 and use all of these to paint a picture of star formation and to measure the IMFs. We find the following: (1) Most of the massive stars are born during a period Delta(Tau) < 3 Myr in each association. Some star formation has clearly preceded this event, as evidenced by the occasional presence of evolved (Tau ~ 10 Myr) 15 Msun stars despite a typical age Tau ~ 2 Myr for the more massive population. However, all these regions also show evidence of 5-10 Msun pre-main-sequence stars (Tau < 1 Myr), demonstrating that some star formation at lower masses does continue for at least 1 Myr after the formation of high-mass stars. (2) There is no statistically significant difference in IMF slopes among these clusters, and the average value is found to be Gamma = -1.1 +/- 0.1 for stars with masses > 7 Msun. A comparison with similarly studied OB associations in the Magellanic Clouds reveals no difference in IMF slope, and hence we conclude that star formation of massive stars in clusters proceeds independently of metallicity, at least between z = 0.02 and z = 0.002. The masses of the highest mass stars are approximately equal in the Milky Way, LMC, and SMC associations, contrary to the expectation that this value should vary by a factor of 3 over this metallicity range. We conclude that radiation pressure on grains must not limit the mass of the highest mass star that can form, in accord with the suggestion of Wolfire & Cassinelli that the mere existence of massive stars suggests that shocks or other mechanisms have disrupted grains in star-forming events. (3) The four Wolf-Rayet stars in our sample have come from stars more massive than 40 Msun; one WC star and one late-type WN star each appear to have come from very massive (~100 Msun) progenitors.
1818. Objects of 1988 Zenith Sky Survey
ID:
ivo://CDS.VizieR/J/AZh/71/352
Title:
Objects of 1988 Zenith Sky Survey
Short Name:
J/AZh/71/352
Date:
21 Oct 2021
Publisher:
CDS
Description:
The results of optical identification of radio sources Zenith Sky Survey with the Palomar Sky Survey prints are presented. The sky survey was conducted with a RATAN-600 radio telescope at 8.0cm in a ring-aperture operation mode. All the objects belong to the radio source population with flux densities in a range from 5 to 50mJy. The mean value of the spectral index distribution for the sources identified with other catalogs was found to be equal to -0.9 at 8.0cm.
1819. Obscured AGN at 1.5<z<3.0
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.
1820. Observational properties of Hipparcos stars
ID:
ivo://CDS.VizieR/J/A+A/595/A59
Title:
Observational properties of Hipparcos stars
Short Name:
J/A+A/595/A59
Date:
21 Oct 2021
Publisher:
CDS
Description:
Since the release of the Hipparcos catalogue in 1997, the distance to the Pleiades open cluster has been heavily debated. The distance obtained from Hipparcos and those by alternative methods differ by 10 to 15%. As accurate stellar distances are key to understanding stellar structure and evolution, this dilemma puts the validity of some stellar evolution models into question. Using our model-independent method to determine parallaxes based on twin stars, we report individual parallaxes of 15 FGK type stars in the Pleiades in anticipation of the astrometric mission Gaia. These parallaxes give a mean cluster parallax of 7.42+/-0.09mas,which corresponds to a mean cluster distance of 134.8+/-1.7pc. This value agrees with the current results obtained from stellar evolution models.