91 research outputs found
On the triple origin of blue stragglers
Blue straggler stars (BSSs) are stars observed to be hotter and bluer than
other stars with the same luminosity in their environment. As such they appear
to be much younger than the rest of the stellar population. Two main channels
have been suggested to produce such stars: (1) collisions between stars in
clusters or (2) mass transfer between, or merger of, the components of
primordial short-period binaries. Here we suggest a third scenario, in which
the progenitor of BSSs are formed in primordial (or dynamically formed)
hierarchical triple stars. In such configurations the dynamical evolution of
the triples through the Kozai mechanism and tidal friction can induce the
formation of very close inner binaries. Angular momentum loss in a magnetized
wind or stellar evolution could then lead to the merger of these binaries (or
to mass transfer between them) and produce BSSs in binary (or triple) systems.
We study this mechanism and its implications and show that it could naturally
explain many of the characteristics of the BSS population in clusters, most
notably the large binary fraction of long period BSS binaries; their unique
period-eccentricity distribution (with typical periods > 700 days); and the
typical location of these BSSs in the color-magnitude diagram, far from the
cluster turn-off point of their host clusters. We suggest that this scenario
has a major (possibly dominant) role in the formation of BSSs in open clusters
and give specific predictions for the the BSSs population formed in this
manner. We also note that triple systems may be the progenitors of the
brightest planetary nebulae in old elliptical galaxies, which possibly evolved
from BSSs.Comment: 10 pages, 6 figures. Minor additions; ApJ, in pres
Photometric Observations of Three High Mass X-Ray Binaries and a Search for Variations Induced by Orbital Motion
We searched for long period variation in V-band, Ic-band and RXTE X-ray light
curves of the High Mass X-ray Binaries (HMXBs) LS 1698 / RX J1037.5-5647, HD
110432 / 1H 1249-637 and HD 161103 / RX J1744.7-2713 in an attempt to discover
orbitally induced variation. Data were obtained primarily from the ASAS
database and were supplemented by shorter term observations made with the 24-
and 40-inch ANU telescopes and one of the robotic PROMPT telescopes. Fourier
periodograms suggested the existence of long period variation in the V-band
light curves of all three HMXBs, however folding the data at those periods did
not reveal convincing periodic variation. At this point we cannot rule out the
existence of long term V-band variation for these three sources and hints of
longer term variation may be seen in the higher precision PROMPT data. Long
term V-band observations, on the order of several years, taken at a frequency
of at least once per week and with a precision of 0.01 mag, therefore still
have a chance of revealing long term variation in these three HMXBs.Comment: Accepted, RAA, May, 201
SDWFS-MT-1: A Self-Obscured Luminous Supernova at z~0.2
We report the discovery of a six-month-long mid-infrared transient,
SDWFS-MT-1 (aka SN 2007va), in the Spitzer Deep, Wide-Field Survey of the NOAO
Deep Wide-Field Survey Bootes field. The transient, located in a z=0.19 low
luminosity (M_[4.5]~-18.6 mag, L/L_MilkyWay~0.01) metal-poor (12+log(O/H)~7.8)
irregular galaxy, peaked at a mid-infrared absolute magnitude of M_[4.5]~-24.2
in the 4.5 micron Spitzer/IRAC band and emitted a total energy of at least
10^51 ergs. The optical emission was likely fainter than the mid-infrared,
although our constraints on the optical emission are poor because the transient
peaked when the source was "behind" the Sun. The Spitzer data are consistent
with emission by a modified black body with a temperature of ~1350 K. We rule
out a number of scenarios for the origin of the transient such as a Galactic
star, AGN activity, GRB, tidal disruption of a star by a black hole and
gravitational lensing. The most plausible scenario is a supernova exploding
inside a massive, optically thick circumstellar medium, composed of multiple
shells of previously ejected material. If the proposed scenario is correct,
then a significant fraction (~10%) of the most luminous supernova may be
self-enshrouded by dust not only before but also after the supernova occurs.
The spectral energy distribution of the progenitor of such a supernova would be
a slightly cooler version of eta Carina, peaking at 20-30 microns.Comment: 26 pages, 5 figures, 1 table, accepted for publication in Ap
Five Kepler target stars that show multiple transiting exoplanet candidates
We present and discuss five candidate exoplanetary systems identified with
the Kepler spacecraft. These five systems show transits from multiple exoplanet
candidates. Should these objects prove to be planetary in nature, then these
five systems open new opportunities for the field of exoplanets and provide new
insights into the formation and dynamical evolution of planetary systems. We
discuss the methods used to identify multiple transiting objects from the
Kepler photometry as well as the false-positive rejection methods that have
been applied to these data. One system shows transits from three distinct
objects while the remaining four systems show transits from two objects. Three
systems have planet candidates that are near mean motion
commensurabilities---two near 2:1 and one just outside 5:2. We discuss the
implications that multitransiting systems have on the distribution of orbital
inclinations in planetary systems, and hence their dynamical histories; as well
as their likely masses and chemical compositions. A Monte Carlo study indicates
that, with additional data, most of these systems should exhibit detectable
transit timing variations (TTV) due to gravitational interactions---though none
are apparent in these data. We also discuss new challenges that arise in TTV
analyses due to the presence of more than two planets in a system.Comment: Accepted to Ap
The Araucaria Project: Improving the cosmic distance scale
The book consists of a number of short articles that present achievements of
the Araucaria members, collaborators, and friends, in various aspects of
distance determinations and related topics. It celebrates the 20-year
anniversary of the Araucaria Project, acknowledges the people who worked for
its success, and popularises our methods and results among broader readership.
This book is a part of a project that has received funding from the European
Union's Horizon 2020 research and innovation programme under grant agreement No
695099.Comment: 114 pages, book published in 2021 on behalf of the Nicolaus
Copernicus Astronomical Center of the Polish Academy of Sciences, to
celebrate 20 years of the Arauria Projec
Recommended from our members
Surface brightness-colour relations of dwarf stars from detached eclipsing binaries: I. Calibrating sample
Aims. Surface brightness - colour relations (SBCRs) are very useful tools for predicting the angular diameters of stars. They offer the possibility to calculate very precise spectrophotometric distances by the eclipsing binary method or the Baade-Wesselink method. Double-lined Detached Eclipsing Binary stars (SB2 DEBs) with precisely known trigonometric parallaxes allow for a calibration of SBCRs with unprecedented precision. In order to improve such calibrations, it is important to enlarge the calibration sample of suitable eclipsing binaries with very precisely determined physical parameters. Methods. We carefully chose a sample of ten SB2 DEBs in the solar neighbourhood which contain inactive main-sequence components. The components have spectral types from early A to early K. All systems have high-precision parallaxes from the Gaia mission. We analysed high precision ground- and space-based photometry simultaneously with the radial velocity curves derived from HARPS spectra. We used spectral disentangling to obtain the individual spectra of the components and used these to derive precise atmospheric parameters and chemical abundances. For almost all components, we derived precise surface temperatures and metallicities. Results. We derived absolute dimensions for 20 stars with an average precision of 0.2% and 0.5% for masses and radii, respectively. Three systems show slow apsidal motion. One system, HD 32129, is most likely a triple system with a much fainter K6V companion. Also three systems contain metallic-line components and show strong enhancements of barium and ittrium. Conclusions. The components of all systems compare well to the SBCR derived before from the detached eclipsing binary stars. With a possible exception of HD 32129, they can be used to calibrate SBCRs with a precision better than 1% with available Gaia DR3 parallaxes
The LAGUNA design study- towards giant liquid based underground detectors for neutrino physics and astrophysics and proton decay searches
The feasibility of a next generation neutrino observatory in Europe is being
considered within the LAGUNA design study. To accommodate giant neutrino
detectors and shield them from cosmic rays, a new very large underground
infrastructure is required. Seven potential candidate sites in different parts
of Europe and at several distances from CERN are being studied: Boulby (UK),
Canfranc (Spain), Fr\'ejus (France/Italy), Pyh\"asalmi (Finland),
Polkowice-Sieroszowice (Poland), Slanic (Romania) and Umbria (Italy). The
design study aims at the comprehensive and coordinated technical assessment of
each site, at a coherent cost estimation, and at a prioritization of the sites
within the summer 2010.Comment: 5 pages, contribution to the Workshop "European Strategy for Future
Neutrino Physics", CERN, Oct. 200
A Comparison of DSM-IV and DSM-5 Panel Members' Financial Associations with Industry: A Pernicious Problem Persists
Lisa Cosgrove and Sheldon Krimsky examine the new competing interest disclosure policy of the American Psychiatric Association (APA) and report that DSM panel members still have considerable financial conflicts of interest
Evaluation of the biomarker candidate MFAP4 for non-invasive assessment of hepatic fibrosis in hepatitis C patients
Cyclical period changes in HT Cas: a clear difference between systems above and below the period gap
We report the identification of cyclical changes in the orbital period of the
eclipsing cataclysmic variable HT Cas. We measured new white dwarf mid-eclipse
timings and combined with published measurements to construct an
observed-minus-calculated diagram covering 29 years of observations. The data
present cyclical variations that can be fitted by a linear plus sinusoidal
function with period 36 yr and semi-amplitude ~ 40 s. The statistical
significance of this period by an F-test is larger than 99.9 per cent. We
combine our results with those in the literature to revisit the issue of
cyclical period changes in cataclysmic variables and their interpretation in
terms of a solar-type magnetic activity cycle in the secondary star. A diagram
of fractional period change (Delta P/P) versus the angular velocity of the
active star (Omega) for cataclysmic variables, RS CVn, W UMa and Algols reveal
that close binaries with periods above the gap (secondaries with convective
envelopes) satisfy a relationship Delta P/P \propto Omega^{-0.7+/-0.1}.
Cataclysmic variables below the period gap (with fully convective secondaries)
deviate from this relationship by more than 3-sigma, with average fractional
period changes ~ 5 times smaller than those of the systems above the gap.Comment: Submitted to Astronomy & Astrophysics (7 pages and 3 figures
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