- 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.
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- 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/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.
- ID:
- ivo://CDS.VizieR/J/ApJ/875/124
- Title:
- Binary red supergiants. II. B-type companions
- Short Name:
- J/ApJ/875/124
- Date:
- 20 Jan 2022 11:13:46
- Publisher:
- CDS
- Description:
- The percentage of massive main-sequence OB stars in binary systems is thought to be as high as 100%. However, very few Galactic binary red supergiants (RSGs) have been identified, despite the fact that these stars are the evolved descendants of OB stars. As shown in our recent paper, binary RSGs will likely have B-type companions, as dictated by stellar evolution considerations. Such a system will have a very unique photometric signature due to the shape of the spectral energy distribution. Using photometric cutoffs, it should therefore be possible to detect candidate RSG+B star binary systems. Here we present our spectroscopic follow-up observations of such candidates. Out of our initial list of 280 candidates in M31 and M33, we observed 149 and confirmed 63 as newly discovered RSG+B star binary systems. Additional spectra of four candidate systems in the Small Magellanic Cloud confirmed all of them as new RSG+B star binaries including the first known RSG+Be star system. By fitting BSTAR06 and MARCS model atmospheres to the newly obtained spectra, we place estimates on the temperatures and subtypes of both the B stars and RSGs. Overall, we have found 87 new RSG+B star binary systems in M31, M33 and the Small and Large Magellanic Clouds. Our future studies are aimed at determining the binary fraction of RSGs.
- ID:
- ivo://CDS.VizieR/J/ApJ/742/48
- Title:
- Blanco survey of the lens BCS J2352-5452
- Short Name:
- J/ApJ/742/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the serendipitous discovery in the Blanco Cosmology Survey (BCS) imaging data of a z=0.9057 galaxy that is being strongly lensed by a massive galaxy cluster at a redshift of z=0.3838. The lens (BCS J2352-5452) was discovered while examining i- and z-band images being acquired in 2006 October during a BCS observing run. Follow-up spectroscopic observations with the Gemini Multi-Object Spectrograph instrument on the Gemini-South 8m telescope confirmed the lensing nature of this system. Using weak-plus-strong lensing, velocity dispersion, cluster richness N_200_, and fitting to a Navarro-Frenk-White (NFW) cluster mass density profile, we have made three independent estimates of the mass M_200_ which are all very consistent with each other. The combination of the results from the three methods gives M_200_=(5.1+/-1.3)x10^14^M_{sun}_, which is fully consistent with the individual measurements. The final NFW concentration c_200_ from the combined fit is c_200_=5.4^+1.4^_-1.1_. We have compared our measurements of M_200_ and c_200_ with predictions for (1) clusters from {Lambda}CDM simulations, (2) lensing-selected clusters from simulations, and (3) a real sample of cluster lenses.
- ID:
- ivo://CDS.VizieR/J/A+A/373/24
- Title:
- Blue compact galaxies from SBS
- Short Name:
- J/A+A/373/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The work studies of the environment of low-mass galaxies with active star formation (SF) and a possible trigger of SF bursts due to gravitational interaction. Following the study by Taylor et al. (1995ApJS...99..427T), we extend the search for possible disturbing galaxies of various masses to a much larger sample of 86 BCGs from the sky region of the Second Byurakan survey (SBS). The BCG magnitudes and radial velocities are revised and up-dated. The sample under study is separated by the criteria: EW([O III]5007)>45{AA} and V_h_<6000km/s nd should be representative of all low-mass galaxies which experience SF bursts.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/81
- Title:
- Bright metal-poor stars from HES Survey. II.
- Short Name:
- J/ApJ/835/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain estimates of stellar atmospheric parameters for a previously published sample of 1777 relatively bright (9<B<14) metal-poor candidates from the Hamburg/ESO Survey. The original Frebel+ (2006, J/ApJ/652/1585; Paper I) analysis of these stars was able to derive estimates of [Fe/H] and [C/Fe] only for a subset of the sample, due to limitations in the methodology then available. A new spectroscopic analysis pipeline has been used to obtain estimates of T_eff_, logg, [Fe/H], and [C/Fe] for almost the entire data set. This sample is very local-about 90% of the stars are located within 0.5kpc of the Sun. We consider the chemodynamical properties of these stars in concert with a similarly local sample of stars from a recent analysis of the Bidelman and MacConnell "weak metal" candidates by Beers+ (2014, J/ApJ/794/58). We use this combined sample to identify possible members of the halo stream of stars suggested by Helmi+ (1999Natur.402...53H) and Chiba & Beers (2000AJ....119.2843C), as well as stars that may be associated with stripped debris from the putative parent dwarf of the globular cluster Omega Centauri, suggested to exist by previous authors. We identify a clear increase in the cumulative frequency of carbon-enhanced metal-poor (CEMP) stars with declining metallicity, as well as an increase in the fraction of CEMP stars with distance from the Galactic plane, consistent with previous results. We also identify a relatively large number of CEMP stars with kinematics consistent with the metal-weak thick-disk population, with possible implications for its origin.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/268
- Title:
- Bright QSOs in Southern Hemisphere (QUBRICS)
- Short Name:
- J/ApJ/887/268
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The study of absorptions along the lines of sight to bright high-z QSOs is an invaluable cosmological tool that provides a wealth of information on the inter-/circum-galactic medium, dark matter, primordial elements, reionization, fundamental constants, and general relativity. Unfortunately, the number of bright (i<~18) QSOs at z>~2 in the southern hemisphere is much lower than that in the north, due to the lack of wide multiwavelength surveys at decl. {delta}<0{deg}, hampering the effectiveness of observations from southern observatories. In this work we present a new method based on Canonical Correlation Analysis to identify such objects, taking advantage of a number of available databases: Skymapper, Gaia DR2, WISE, and 2MASS. Our QSO candidate sample lists 1476 sources with i<18 over 12400deg^2^ in the southern hemisphere. With a preliminary campaign we observed spectroscopically 69 of them, confirming 54 new bright QSOs at z>2.5, corresponding to a success rate of our method of ~80%. Furthermore, we estimate a completeness of ~90% of our sample at completion of our observation campaign. The new QSOs confirmed by this first and the forthcoming campaigns (QUBRICS survey) will be the targets of subsequent studies using higher resolution spectrographs, like ESPRESSO, UVES, and (in the long term) ELT/HIRES.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/8
- Title:
- BVI LCs and radial velocities of PSR J1306-40
- Short Name:
- J/ApJ/876/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- PSR J1306-40 is a millisecond pulsar (MSP) binary with a non-degenerate companion in an unusually long ~1.097 day orbit. We present new optical photometry and spectroscopy of this system, and model these data to constrain fundamental properties of the binary such as the component masses and distance. The optical data imply a minimum neutron star mass of 1.75+/-0.09M_{sun}_ (1{sigma}) and a high, nearly edge-on inclination. The light curves suggest a large hot spot on the companion, suggestive of a portion of the pulsar wind being channeled to the stellar surface by the magnetic field of the secondary, mediated via an intrabinary shock. The H{alpha} line profiles switch rapidly from emission to absorption near the companion inferior conjunction, consistent with an eclipse of the compact emission region at these phases. At our optically inferred distance of 4.7+/-0.5kpc, the X-ray luminosity is ~10^33^erg/s, brighter than nearly all known redbacks in the pulsar state. The long-period, subgiant-like secondary, and luminous X-ray emission suggest this system may be part of the expanding class of MSP binaries that are progenitors to typical field pulsar-white dwarf binaries.