134 research outputs found
LMC S154: the first Magellanic symbiotic recurrent nova
Classical nova outburst has been suggested for a number of extragalactic
symbiotic stars, but in none of the systems has it been proven. In this work we
study the nature of one of these systems, LMC S154. We gathered archival
photometric observations in order to determine the timescales and nature of
variability in this system. Additionally we carried out photometric and
spectroscopic monitoring of the system and fitted synthetic spectra to the
observations. Carbon abundance in the photosphere of the red giant is
significantly higher than that derived for the nebula, which confirms pollution
of the circumbinary material by the ejecta from nova outburst. The photometric
and spectroscopic data show that the system reached quiescence in 2009, which
means that for the first time all of the phases of a nova outburst were
observed in an extragalactic symbiotic star. The data indicate that most
probably there were three outbursts observed in LMC S154, which would make this
system a member of a rare class of symbiotic recurrent novae. The recurrent
nature of the system is supported by the discovery of coronal lines in the
spectra, which are observed only in symbiotic stars with massive white dwarfs
and with short-recurrence-time outbursts. Gathered evidence is sufficient to
classify LMC S154 as the first bona fide extragalactic symbiotic nova, which is
likely a recurrent nova. It is also the first nova with a carbon-rich donor.Comment: 16 pages, 7 figures, accepted for publication in A&
Identifying and characterizing ultracool dwarfs ejected from post-encounter disintegrating systems
Disintegrating multiple systems have been previously discovered from
kinematic studies of the catalogue. They are presumably the
result of dynamical encounters taking place in the Galactic disk between
single/multiple systems. In this paper, we aim to expand the search for such
systems, to study their properties, as well as to characterize possible
low-mass ejecta (i.e. brown dwarfs and planets). We have assembled a list of 15
candidate systems using astrometry from the Tycho-Gaia astrometric solution
(later upgraded with DR3), and here we present the discovery and
follow-up of 5 of them. We have obtained DECam imaging for all 5 systems and by
combining near-infrared photometry and proper motion, we searched for
ultra-cool ejected components. We find that the system consisting of TYC
7731-1951-1, TYC 7731-2128 AB, and TYC 7731-1995-1ABC?, contains one very
promising ultra-cool dwarf candidate. Using additional data from the
literature, we have found that 3 out of 5 disintegrating system candidates are
likely to be true disintegrating systems.Comment: Accepted for publication in MNRAS. 17 pages, 8 figures, 4 table
Caltech-NRAO Stripe 82 Survey (CNSS) Paper V: AGNs that transitioned toradio-loud state
A recent multi-year Caltech-NRAO Stripe 82 Survey (CNSS) revealed a group of objects that appeared as new radio sources after >5--20 years of absence. They are transient phenomena with respect to the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey and constitute the first unbiased sample of renewed radio activity. Here we present the follow-up, radio, optical and X-ray study of them. The group consist of 12 sources, both quasars and galaxies with wide redshift (0.04 24.5) distribution. Their radio properties in the first phase of activity, namely the convex spectra and compact morphology, allow them all to be classified as gigahertz-peaked spectrum (GPS) sources. We conclude that the spectral changes are a consequence of the evolution of newly-born radio jets. Our observations show that over the next few years of activity the GPS galaxies keep the convex shape of the spectrum, while GPS quasars rapidly transform into flat-spectrum sources, which may result in them not being recognized as young sources. The wide range of bolometric luminosities, black hole masses and jet powers among the transient sources indicates even greater population diversity in the group of young radio objects. We also suggest that small changes of the accretion disc luminosity (accretion rate) may be sufficient to ignite low-power radio activity that evolves on the scale of decades
Massive open star clusters using the VVV survey : V. Young clusters with an OB stellar population
Context. The ESO public survey VISTA Variables in the VÃa Láctea (VVV) has contributed with deep multi-epoch photometry of the Galactic bulge and the adjacent part of the disk over 526 sq. deg. More than a hundred cluster candidates have been reported thanks to this survey. Aims. We present the fifth article in a series of papers focused on young and massive clusters discovered in the VVV survey. In this paper, we present the physical characterization of five clusters with a spectroscopically confirmed OB-type stellar population. Methods. To characterize the clusters, we used near-infrared photometry (J, H, and KS) from the VVV survey and near-infrared K-band spectroscopy from ISAAC at VLT, following the methodology presented in the previous articles of the series. Results. All clusters in our sample are very young (ages between 1–20 Myr), and their total mass are between (1.07+0.40 −0.30) × 102 M and (4.17+4.15 −2.08) × 103 M . We observed a relation between the clusters total mass Mecl and the mass of their most massive stellar member mmax, for clusters with an age <10 Myr
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