- ID:
- ivo://CDS.VizieR/J/AJ/155/240
- Title:
- A spectroscopic survey of field RHB stars
- Short Name:
- J/AJ/155/240
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A metallicity, chemical composition, and kinematic survey has been conducted for a sample of 340 candidate field red horizontal-branch (RHB) stars. Spectra with high resolution and high signal-to-noise ratio were gathered with the McDonald Observatory 2.7 m Tull and the Hobby-Eberly Telescope echelle spectrographs, and were used to determine effective temperatures, surface gravities, microturbulent velocities, [Fe/H] metallicities, and abundance ratios [X/Fe] for seven {alpha} and Fe-group species. The derived temperatures and gravities confirm that at least half of the candidates are true RHB stars, with (average) parameters T_eff_~5000 K and log g~2.5. From the {alpha} abundances alone, the thin and thick Galactic populations are apparent in our sample. Space motions for 90% of the program stars were computed from Hipparcos and Gaia parallaxes and proper motions. Correlations between chemical compositions and Galactic kinematics clearly indicate the existence of both thin-disk and thick-disk RHB stars.
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- ID:
- ivo://CDS.VizieR/J/A+A/653/A134
- Title:
- AT 2018bwo light curves
- Short Name:
- J/A+A/653/A134
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Luminous red novae (LRNe) are astrophysical transients associated with the partial ejection of a binary system's common envelope (CE) shortly before its merger. Here we present the results of our photometric and spectroscopic follow-up campaign of AT 2018bwo (DLT 18x), a LRN discovered in NGC 45, and investigate its progenitor system using binary stellar-evolution models. The transient reached a peak magnitude of M_r_=-10.97+/-0.11 and maintained this brightness during its optical plateau of t_p_=41+/-5d ays. During this phase, it showed a rather stable photospheric temperature of ~3300K and a luminosity of ~10^40^erg/s. Although the luminosity and duration of AT 2018bwo is comparable to the LRNe V838 Mon and M31-2015LRN, its photosphere at early times appears larger and cooler, likely due to an extended mass-loss episode before the merger. Toward the end of the plateau, optical spectra showed a reddened continuum with strong molecular absorption bands. The IR spectrum at +103 days after discovery was comparable to that of an M8.5 II type star, analogous to an extended AGB star. The reprocessed emission by the cooling dust was also detected in the mid-infrared bands ~1.5 years after the outburst. Archival Spitzer and Hubble Space Telescope data taken 10-14yrs before the transient event suggest a progenitor star with T_prog_~6500K, R_prog_~100R_{sun}_, and L_prog_=2x10^4^L_{sun}_, and an upper limit for optically thin warm (1000K) dust mass of M_d_<10^-6^M_{sun}_. Using stellar binary-evolution models, we determined the properties of binary systems consistent with the progenitor parameter space. For AT 2018bwo, we infer a primary mass of 12-16M_{sun}_, which is 9-45% larger than the ~11M_{sun}_ obtained using single-star evolution models. The system, consistent with a yellow-supergiant primary, was likely in a stable mass-transfer regime with -2.4 <= log (M_dot/Msun /yr) <= -1.2 a decade before the main instability occurred. During the dynamical merger, the system would have ejected 0.15-0.5M_{sun}_ with a velocity of ~500km/s.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A93
- Title:
- AT 2020hat and AT 2020kog light curves
- Short Name:
- J/A+A/647/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our monitoring campaigns of the luminous red novae (LRNe) AT 2020hat in NGC 5068 and AT 2020kog in NGC 6106. The two objects were imaged (and detected) before their discovery by routine survey operations. They show a general trend of slow luminosity rise lasting at least a few months. The subsequent major LRN outbursts were extensively followed in photometry and spectroscopy. The light curves present an initial short-duration peak, followed by a redder plateau phase. AT 2020kog is a moderately luminous event peaking at ~7x10^40^erg/s, while AT 2020hat is almost one order of magnitude fainter than AT 2020kog, although it is still more luminous than V838 Mon. In analogy with other LRNe, the spectra of AT 2020kog change significantly with time. They resemble those of type IIn supernovae at early phases, then they become similar to those of K-type stars during the plateau, and to M-type stars at very late phases. In contrast, AT 2020hat already shows a redder continuum at early epochs, and its spectrum shows the late appearance of molecular bands. A moderate-resolution spectrum of AT 2020hat taken at +37d after maximum shows a forest of narrow P Cygni lines of metals with velocities of 180 km/s, along with an Halpha emission with a full-width at half-maximum velocity of 250km/s. For AT 2020hat, a robust constraint on its quiescent progenitor is provided by archival images of the Hubble Space Telescope. The progenitor is clearly detected as a mid-K type star, with an absolute magnitude of M_F606W=-3.33+/-0.09mag and a colour of F606W-F814W=1.14+/-0.05mag, which are inconsistent with the expectations from a massive star that could later produce a core-collapse supernova. Although quite peculiar, the two objects nicely match the progenitor versus light curve absolute magnitude correlations discussed in the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/632/L6
- Title:
- AT 2018hso light curves and spectra
- Short Name:
- J/A+A/632/L6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The absolute magnitudes of luminous red novae (LRNe) are intermediate between those of novae and supernovae (SNe), and show a relatively homogeneous spectro-photometric evolution. Although they were thought to derive from core instabilities in single stars, there is growing support for the idea that they are triggered by binary interaction that possibly ends with the merging of the two stars. AT 2018hso is a new transient showing transitional properties between those of LRNe and the class of intermediate-luminosity red transients (ILRTs) similar to SN 2008S. Through the detailed analysis of the observed parameters, our study support that it actually belongs to the LRN class and was likely produced by the coalescence of two massive stars. We obtained ten months of optical and near-infrared photometric monitoring, and 11 epochs of low-resolution optical spectroscopy of AT 2018hso. We compared its observed properties with those of other ILRTs and LRNe. We also inspected the archival Hubble Space Telescope (HST) images obtained about 15 years ago to constrain the progenitor properties. The light curves of AT 2018hso show a first sharp peak (reddening-corrected M_r_=13.93mag), followed by a broader and shallower second peak that resembles a plateau in the optical bands. The spectra dramatically change with time. Early-time spectra show prominent Balmer emission lines and a weak [CaII] doublet, which is usually observed in ILRTs. However, the strong decrease in the continuum temperature, the appearance of narrow metal absorption lines, the great change in the H{alpha} strength and profile, and the emergence of molecular bands support an LRN classification. The possible detection of a M_I_~8mag source at the position of AT 2018hso in HST archive images is consistent with expectations for a pre-merger massive binary, similar to the precursor of the 2015 LRN in M101. We provide reasonable arguments to support an LRN classification for AT 2018hso. This study reveals growing heterogeneity in the observables of LRNe than has been thought previously, which is a challenge for distinguishing between LRNe and ILRTs. This suggests that the entire evolution of gap transients needs to be monitored to avoid misclassifications.
- ID:
- ivo://CDS.VizieR/J/AJ/157/153
- Title:
- Atomic lines in spectra of RR Lyrae & RHB stars
- Short Name:
- J/AJ/157/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived relations between FWHMs and equivalent widths of metallic absorption lines in the spectra of RR Lyrae stars to estimate new upper limits on the axial equatorial rotational velocities of RR Lyrae and metal-poor red horizontal branch (RHB) stars. We have also derived the variations of RR Lyrae macroturbulent velocities during the pulsation cycles. In RRab cycles, the line widths are dominated by phase-dependent convolutions of axial rotation and macroturbulence, which we designate as V_macrot_. The behavior of V_macrot_ is remarkably uniform among the RRab stars, but the behavior of V_macrot_ among RRc stars varies strongly from star to star. The RRab stars exhibit an upper limit on V_macrot_ of 5+/-1 km/s with weak evidence of an anticorrelation with T_eff_. The RRc minima range from 2 to 12 km/s. The abrupt decline in large rotations with decreasing T_eff_ at the blue boundary of the instability strip and the apparently smooth continuous variation among the RRab and RHB stars suggests that HB stars gain/lose surface angular momentum on timescales that are short compared to HB lifetimes. The V_macrot_ values for our metal-poor RHB stars agree well with those derived by Fourier analysis of an independent but less metal-poor sample of Carney et al. (2008AJ....135..892C); they conform qualitatively to the expectations of Tanner et al. (2013ApJ...778..117T). A general conclusion of our investigation is that surface angular momentum as measured by V_rot_sin(i) is not a reliable indicator of total stellar angular momentum anywhere along the HB.
- ID:
- ivo://CDS.VizieR/J/ApJ/484/394
- Title:
- AX Mon photometry and UV spectra
- Short Name:
- J/ApJ/484/394
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- AX Monocerotis is a 232d, noneclipsing, interacting binary star that consists of a K giant, a Be-like giant, and a large amounts of circumstellar material. The K star is almost certainly a synchronous rotator and is probably in contact with its critical lobe. The Be star was believed to be a rapid rotator based on extremely wide absorption lines, but new spectra show that these lines arise from the circumstellar environment. Hydrogen emission, also circumstellar, is many times stronger than the continuum. Near-ultraviolet light curves exhibit a 0.5 mag dip near phase 0.75, but there is no such variability at longer wavelengths. Gas flow trajectories from the cusp of the K star toward the Be star provide a simple explanation for the photometric and spectroscopic behavior. We may have found a decreasing orbital period, but more data are necessary to confirm this result. We present several models for AX Mon based on (1) new and archival visible photometry, (2) archival ultraviolet spectroscopy, (3) new and archival visible spectroscopy, (4) new visible polarimetry, and (5) new radio photometry. Further observations, including optical interferometry, are proposed.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/49
- Title:
- A 10yr reverberation mapping campaign for 3C273
- Short Name:
- J/ApJ/876/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite many decades of study, the kinematics of the broad-line region of 3C 273 are still poorly understood. We report a new, high signal-to-noise, reverberation mapping campaign carried out from 2008 November to 2018 March that allows the determination of time lags between emission lines and the variable continuum with high precision. The time lag of variations in H{beta} relative to those of the 5100{AA} continuum is 146.8_-12.1_^+8.3^days in the rest frame, which agrees very well with the Paschen-{alpha} region measured by the GRAVITY at The Very Large Telescope Interferometer. The time lag of the H{gamma} emission line is found to be nearly the same as that for H{beta}. The lag of the FeII emission is 322.0_-57.9_^+55.5^days, longer by a factor of ~2 than that of the Balmer lines. The velocity-resolved lag measurements of the H{beta} line show a complex structure that can be possibly explained by a rotation-dominated disk with some inflowing radial velocity in the H{beta}-emitting region. Taking the virial factor of f_BLR_=1.3, we derive a BH mass of dM/dt=4.1_-0.4_^+0.3^x10^8^M_{sun}_ and an accretion rate of 9.3L_Edd_c^-2^ from the H{beta} line. The decomposition of its Hubble Space Telescope images yields a host stellar mass of M*=10^11.3+/-0.7^M_{sun}_, and a ratio of dM/dt/M*~2.0x10^-3^ in agreement with the Magorrian relation. In the near future, it is expected to compare the geometrically thick BLR discovered by the GRAVITY in 3C 273 with its spatially resolved torus in order to understand the potential connection between the BLR and the torus.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/50
- Title:
- Barium abundances of red giant branch stars
- Short Name:
- J/ApJ/869/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There are many candidate sites of the r-process: core-collapse supernovae (CCSNe; including rare magnetorotational core-collapse supernovae), neutron star mergers (NSMs), and neutron star/black hole mergers. The chemical enrichment of galaxies --specifically dwarf galaxies-- helps distinguish between these sources based on the continual build-up of r-process elements. This technique can distinguish between the r-process candidate sites by the clearest observational difference --how quickly these events occur after the stars are created. The existence of several nearby dwarf galaxies allows us to measure robust chemical abundances for galaxies with different star formation histories. Dwarf galaxies are especially useful because simple chemical evolution models can be used to determine the sources of r-process material. We have measured the r-process element barium with Keck/DEIMOS medium-resolution spectroscopy. We present the largest sample of barium abundances (almost 250 stars) in dwarf galaxies ever assembled. We measure [Ba/Fe] as a function of [Fe/H] in this sample and compare with existing [{alpha}/Fe] measurements. We have found that a large contribution of barium needs to occur at more delayed timescales than CCSNe in order to explain our observed abundances, namely the significantly more positive trend of the r-process component of [Ba/Fe] versus [Fe/H] seen for [Fe/H]<~-1.6 when compared to the [Mg/Fe] versus [Fe/H] trend. We conclude that NSMs are the most likely source of r-process enrichment in dwarf galaxies at early times.
- ID:
- ivo://CDS.VizieR/J/ApJ/881/154
- Title:
- BAT AGN spectroscopic survey. XVI. Blazars
- Short Name:
- J/ApJ/881/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recently released 105-month Swift-Burst Alert Telescope (BAT) all-sky hard X-ray survey catalog presents an opportunity to study astrophysical objects detected in the deepest look at the entire hard X-ray (14-195keV) sky. Here we report the results of a multifrequency study of 146 blazars from this catalog, quadrupling the number compared to past studies, by utilizing recent data from the Fermi-Large Area Telescope (LAT), Swift-BAT, and archival measurements. In our {gamma}-ray analysis of ~10yr of the LAT data, 101 are found as {gamma}-ray emitters, whereas, 45 remains LAT undetected. We model the broadband spectral energy distributions with a synchrotron-inverse Compton radiative model. On average, BAT detected sources host massive black holes (M_bh_~10^9^M_{sun}_) and luminous accretion disks (L_d_~10^46^erg/s). At high redshifts (z>2), BAT blazars host more powerful jets with luminous accretion disks compared to those detected only with Fermi-LAT. We find good agreement in the black hole masses derived from the single-epoch optical spectroscopic measurements and standard accretion disk modeling approaches. Other physical properties of BAT blazars are similar to those known for Fermi-LAT detected objects.
- ID:
- ivo://CDS.VizieR/J/MNRAS/448/2717
- Title:
- Bayesian analysis of resolved stellar spectra
- Short Name:
- J/MNRAS/448/2717
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We introduce a Bayesian method for fitting faint, resolved stellar spectra in order to obtain simultaneous estimates of redshift and stellar-atmospheric parameters. We apply the method to thousands of spectra - covering 5160-5280{AA} at resolution R~20000 - that we have acquired with the MMT/Hectochelle fibre spectrograph for red giant and horizontal branch candidates along the line of sight to the Milky Way's dwarf spheroidal satellite in Draco. The observed stars subtend an area of ~4deg^2^, extending ~3 times beyond Draco's nominal 'tidal' radius. For each spectrum, we tabulate the first four moments - central value, variance, skewness and kurtosis - of posterior probability distribution functions representing estimates of the following physical parameters: line-of-sight velocity (v_los_), effective temperature (T_eff_), surface gravity (logg) and metallicity ([Fe/H]). After rejecting low-quality measurements, we retain a new sample consisting of 2813 independent observations of 1565 unique stars, including 1879 observations for 631 stars with (as many as 13) repeat observations. Parameter estimates have median random errors of v_los_=0.88km/s, T_eff_=162K, {sigma}logg=0.37dex and {sigma}[Fe/H]=0.20dex. Our estimates of physical parameters distinguish ~470 likely Draco members from interlopers in the Galactic foreground.