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821. FAUST sources in NGC 4038-39 and 6752 direction
ID:
ivo://CDS.VizieR/J/MNRAS/324/580
Title:
FAUST sources in NGC 4038-39 and 6752 direction
Short Name:
J/MNRAS/324/580
Date:
21 Oct 2021
Publisher:
CDS
Description:
Analysis of ultraviolet (UV) observations with the FAUST shuttle-borne telescope toward the Antennae and NGC 6752 celestial regions resulted in the detection of 46 and 221 candidate sources respectively, for a signal-to-noise ratio of 8. We discuss the source detection process and the identification of UV sources with optical counterparts. Using correlations with existing catalogues, we present reliable identifications for approximately 60 per cent of the sources. We find that most identified objects are B, A and F stars. The remaining identified objects are galaxies, a white dwarf in a binary system, and two K-type stars. Nearly all of the remaining unidentified objects have assigned optical counterparts but, lacking additional information, we give these only as best estimates. With help from new diagnostic diagrams, we suggest that these unclassified objects are main-sequence (or giant) stars within the local spiral arm or halo; or other hot evolved objects within the local spiral arm. We discuss the nature of the objects found and compare our results with those predicted from spectral and Galactic models.
822. FAUST UV sources towards Ophiuchus
ID:
ivo://CDS.VizieR/J/MNRAS/332/441
Title:
FAUST UV sources towards Ophiuchus
Short Name:
J/MNRAS/332/441
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of an analysis of a UV image in the direction of Ophiuchus, obtained with the FAUST instrument. The image contains 228 UV sources. Most of these are identified as normal early-type stars through correlations with catalogued objects. For the first time in this project we identify UV sources as such stars by selecting suitable candidates in crowded fields as the bluest objects in colour-colour diagrams using observations from the Wise Observatory. These candidates are then studied using low-resolution spectroscopy, which allows the determination of spectral types to an accuracy of about one-half class, for 60 stars. Synthetic photometry of spectral data is performed in order to predict the expected UV emission, on the basis of the photometric information. These results are used along with the Hipparcos/Tycho (<I/239>) information, to search for subluminous stars. The comparison of the predicted emission with the FAUST measured magnitudes allows us to select 12 stars as highly probable evolved hot stars. High signal-to-noise spectra are obtained for nine of these stars, and Balmer line profiles are compared with the prediction of atmosphere models and with the spectrum of real stellar atmospheres. Among the nine candidates, six are classified as previously unrecognized sdB stars, and two as white dwarfs. Our result indicates that indeed more bright subluminous stars are still unrecognized in the existing samples.
823. FCOS Ultra Compact Dwarf galaxies radial vel.
ID:
ivo://CDS.VizieR/J/A+A/418/445
Title:
FCOS Ultra Compact Dwarf galaxies radial vel.
Short Name:
J/A+A/418/445
Date:
21 Oct 2021
Publisher:
CDS
Description:
The relation between the Ultra Compact Dwarf galaxies (hereafter UCDs) recently discovered in the Fornax cluster (Drinkwater et al., 2003Natur.423..519D; Mieske et al., 2002, Cat. <J/A+A/383/823>) and the brightest globular clusters associated with the central galaxy NGC 1399 has been investigated in the spectroscopic Fornax Compact Object Survey FCOS. FCOS was carried out with the 2.5m du Pont telescope at Las Campanas, in the three nights of 2002/12/04 to 2002/12/06. Mieske et al. (2002, Cat. <J/A+A/383/823>) deals with the first part FCOS-1, this paper deals with the larger FCOS-2. The spectral resolution of FCOS was approx. 4{AA}. In the FCOS, 280 unresolved objects with 0<(V-I)<1.5mag in the magnitude space covering UCDs and bright globular clusters (18<V<21mag) were observed spectroscopically, among them 185 in FCOS-2. In the entire FCOS-sample there are five already known UCDs and 54 new Fornax members, 12 from FCOS-1 and 42 from FCOS-2.
824. FeII emission in SDSS type 1 AGNs
ID:
ivo://CDS.VizieR/J/ApJ/736/86
Title:
FeII emission in SDSS type 1 AGNs
Short Name:
J/ApJ/736/86
Date:
21 Oct 2021
Publisher:
CDS
Description:
We used a large, homogeneous sample of 4178 z<=0.8 Seyfert 1 galaxies and QSOs selected from the Sloan Digital Sky Survey to investigate the strength of FeII emission and its correlation with other emission lines and physical parameters of active galactic nuclei. We find that the strongest correlations of almost all the emission-line intensity ratios and equivalent widths (EWs) are with the Eddington ratio (L/L_Edd_), rather than with the continuum luminosity at 5100{AA} (L_5100_) or black hole mass (M_BH_); the only exception is the EW of ultraviolet FeII emission, which does not correlate at all with broad-line width, L_5100_, M_BH_, or L/L_Edd_. By contrast, the intensity ratios of both the ultraviolet and optical FeII emission to MgII{lambda}2800 correlate quite strongly with L/L_Edd_. Interestingly, among all the emission lines in the near-UV and optical studied in this paper (including MgII{lambda}2800, H{beta}, and [OIII]{lambda}5007), the EW of narrow optical FeII emission has the strongest correlation with L/L_Edd_. We hypothesize that the variation of the emission-line strength in active galaxies is regulated by L/L_Edd_ because it governs the global distribution of the hydrogen column density of the clouds gravitationally bound in the line-emitting region, as well as its overall gas supply. The systematic dependence on L/L_Edd_ must be corrected when using the FeII/MgII intensity ratio as a measure of the Fe/Mg abundance ratio to study the history of chemical evolution in QSO environments.
825. Fermi blazars with Doppler factors
ID:
ivo://CDS.VizieR/J/ApJ/835/L38
Title:
Fermi blazars with Doppler factors
Short Name:
J/ApJ/835/L38
Date:
21 Oct 2021
Publisher:
CDS
Description:
Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data. Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between {gamma}-ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi, we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic {gamma}-ray luminosity is strongly correlated with other intrinsic luminosities.
826. 8 Fermi GRB afterglows follow-up
ID:
ivo://CDS.VizieR/J/ApJ/806/52
Title:
8 Fermi GRB afterglows follow-up
Short Name:
J/ApJ/806/52
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Fermi Gamma-ray Space Telescope has greatly expanded the number and energy window of observations of gamma-ray bursts (GRBs). However, the coarse localizations of tens to a hundred square degrees provided by the Fermi GRB Monitor instrument have posed a formidable obstacle to locating the bursts' host galaxies, measuring their redshifts, and tracking their panchromatic afterglows. We have built a target-of-opportunity (TOO) mode for the intermediate Palomar Transient Factory (iPTF) in order to perform targeted searches for Fermi afterglows. Here, we present the results of one year of this program: 8 afterglow discoveries out of 35 searches. Two of the bursts with detected afterglows (GRBs 130702A and 140606B) were at low redshift (z=0.145 and 0.384, respectively) and had spectroscopically confirmed broad-line Type Ic supernovae. We present our broadband follow-up including spectroscopy as well as X-ray, UV, optical, millimeter, and radio observations. We study possible selection effects in the context of the total Fermi and Swift GRB samples. We identify one new outlier on the Amati relation. We find that two bursts are consistent with a mildly relativistic shock breaking out from the progenitor star rather than the ultra-relativistic internal shock mechanism that powers standard cosmological bursts. Finally, in the context of the Zwicky Transient Facility, we discuss how we will continue to expand this effort to find optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo.
827. F, G and K stars BVRI photometry
ID:
ivo://CDS.VizieR/J/A+AS/131/197
Title:
F, G and K stars BVRI photometry
Short Name:
J/A+AS/131/197
Date:
15 Dec 2021 08:12:40
Publisher:
CDS
Description:
We present accurate BV(RI)c photometry for a sample of F, G and K stars detected in selected areas of the ROSAT all-sky survey (RASS). We have used the photometry, in addition to low-resolution spectroscopy, to estimate spectral classifications, distances and X-ray luminosities. The log(L_X_/L_V_) in the sample lies below -2. Although the sample contains also nearby, inactive stars, it is dominated by active objects. The median X-ray luminosity in our sample is <L_X_>=29.88 and the mean value of the hardness ratios <HR1>=0.13+/-0.35. We compare the derived X-ray luminosity function with similar functions obtained from the serendipitous samples of the Einstein Observatory medium sensitivity survey (EMSS, Cat. <IX/15>) and EXOSAT (Cat. <J/A+AS/115/41>). Our sample is completely consistent with the EMSS sample of solar type stars, indicating that both our sources and the EMSS sources are representative of the high galactic latitude X-ray stellar population. We do not find extremely active stars (log(L_X_)>=32), as are found in the EMSS sample, and we argue that these objects are rare.
828. 504 F-G dwarfs photometric metallicities
ID:
ivo://CDS.VizieR/J/other/ApSS/364.172
Title:
504 F-G dwarfs photometric metallicities
Short Name:
J/other/ApSS/364
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this study, photometric metallicity and absolute magnitude calibrations were derived using F-G spectral type main-sequence stars in the Solar neighbourhood with precise spectroscopic, photometric and Gaia astrometric data for UBV photometry. The sample consists of 504 main-sequence stars covering the temperature, surface gravity and colour index intervals 5300<Teff<7300K, logg>4 (cgs) and 0.3<(B-V)0<0.8mag, respectively. Stars with relative trigonometric parallax errors {sigma}_{pi}/{pi}<=0.01 were preferred from Gaia DR2 data for the estimation of their M_V absolute magnitudes. In order to obtain calibrations, (U-B)0 and (B-V)0 colour indices of stars were preferred and a multi-variable second order equation was used. Calibrations are valid for main-sequence stars in the metallicity and absolute magnitude ranges -2<[Fe/H]<0.5dex and 2.5<M_V_<6mag, respectively. The mean value and standard deviation of the differences between original and estimated values for the metal abundance and absolute magnitude are <{Delta}[Fe/H]>=0.00+/-0.11dex and <{Delta}M_V_>=0.00+/-0.22mag, respectively. In this work, it has been shown that more precise iron abundance and absolute magnitude values were obtained with the new calibrations, compared to previous calibrations in the literature.
829. 342 FGK-dwarfs ages using GALEX FUV magnitudes
ID:
ivo://CDS.VizieR/J/AJ/160/217
Title:
342 FGK-dwarfs ages using GALEX FUV magnitudes
Short Name:
J/AJ/160/217
Date:
21 Oct 2021
Publisher:
CDS
Description:
Stellar age cannot be directly measured, yet age determinations are fundamental to understanding the evolution of stars, planets, and galaxies. The work presented here builds upon the idea of a stellar-activity age. We utilized far-ultraviolet (FUV) photometry acquired by the Galaxy Evolution Explorer (GALEX) space telescope as an indicator of chromospheric activity to infer ages of late-F, G, and K type dwarf stars. We derived a purely empirical correlation between FUV magnitudes and stellar age in conjunction with (B-V) color. Our attention is restricted to Sun-like stars with color range 0.55<=(B-V)<=0.71 and absolute magnitude range 4.3<=MV<=5.3. The correlation is defined in terms of a FUV-excess parameter Q(FUV-B,B-V). We related stellar age, {tau}, to Q through the relation log_e_({tau})=log_e_(a)+bQ, where a and b are fit parameters and functions of (B-V). This correlation is functional up to 6Gyr for FGK dwarfs. With such a correlation, one only needs Johnson (B-V) and FUV measurements to estimate the stellar age for Population i dwarf stars of solar-like temperature and metallicity. Such a calibration has utility in population studies of FGK dwarfs for further understanding of the chemical evolution of the Milky Way. As an illustration of one such application, we have constructed activity and FUV-age distributions for a sample of thin and thick disk stars, as distinguished by their chemical abundances. Considerable overlap is found between the activity distribution and age range of the two populations. We discuss the possibility that some high-[{alpha}/Fe] thick disk stars were formed as a result of the accretion of dwarf galaxies as recently as 4Gyr ago.
830. FGK stars magnetic activity in LAMOST-Kepler field
ID:
ivo://CDS.VizieR/J/ApJS/247/9
Title:
FGK stars magnetic activity in LAMOST-Kepler field
Short Name:
J/ApJS/247/9
Date:
21 Oct 2021
Publisher:
CDS
Description:
Monitoring chromospheric and photospheric indexes of magnetic activity can provide valuable information, especially the interaction between different parts of the atmosphere and their response to magnetic fields. We extract chromospheric indexes, S and R_HK_^+^, for 59816 stars from LAMOST spectra in the LAMOST-Kepler program, and photospheric index, Reff, for 5575 stars from Kepler light curves. The log Reff shows positive correlation with logR_HK_^+^. We estimate the power-law indexes between Reff and R_HK_^+^ for F-, G-, and K-type stars, respectively. We also confirm the dependence of both chromospheric and photospheric activity on stellar rotation. Ca ii H and K emissions and photospheric variations generally decrease with increasing rotation periods for stars with rotation periods exceeding a few days. The power-law indexes in exponential decay regimes show different characteristics in the two activity-rotation relations. The updated largest sample including the activity proxies and reported rotation periods provides more information to understand the magnetic activity for cool stars.