244 research outputs found
Astrophysical parameters and orbital solution of the peculiar X-ray transient IGR J00370+6122
BD+6073 is the optical counterpart of the X-ray source IGR J00370+6122, a
probable accretion-powered X-ray pulsar. The X-ray light curve of this binary
system shows clear periodicity at 15.7 d, which has been interpreted as
repeated outbursts around the periastron of an eccentric orbit. We obtained
high-resolution spectra of BD+6073 at different epochs. We used the FASTWind
code to generate a stellar atmosphere model to fit the observed spectrum and
obtain physical magnitudes. The synthetic spectrum was used as a template for
cross-correlation with the observed spectra to measure radial velocities. The
radial velocity curve provided an orbital solution for the system. We have also
analysed the RXTE/ASM and Swift/BAT light curves to confirm the stability of
the periodicity. BD +6073 is a BN0.7 Ib low-luminosity supergiant located at an
approximate distance of 3.1 kpc, in the CasOB4 association. We derive
Teff=24000 K and log gc=3.0, and chemical abundances consistent with a
moderately high level of evolution. The spectroscopic and evolutionary masses
are consistent at the 1 sigma level with a mass of 15 solar masses. The
recurrence time of the X-ray flares is the orbital period of the system. The NS
is in a high eccentricity (e=0.56) orbit, and the X-ray emission is strongly
peaked around orbital phase 0.2, though the observations are consistent with
some level of X-ray activity happening at all orbital phases. The X-ray
behaviour of IGR J00370+6122 is reminiscent of intermediate SFXTs, though its
peak luminosity is rather low. The orbit is somewhat wider than those of
classical persistent supergiant X-ray binaries, which, combined with the low
luminosity of the mass donor, explains the low X-ray luminosity. IGR
J00370+6122 will likely evolve towards a persistent supergiant system,
highlighting the evolutionary connection between different classes of
wind-accreting X-ray sources.Comment: Accepted for publication in A&
The massive multiple system HD 64315
The O6 Vn star HD 64315 is believed to belong to the star-forming region
known as NGC 2467, but previous distance estimates do not support this
association. We explore the multiple nature of this star with the aim of
determining its distance, and understanding its connection to NGC 2467. A total
of 52 high-resolution spectra have been gathered over a decade. We use their
analysis, in combination with the photometric data from All Sky Automated
Survey and Hipparcos catalogues, to conclude that HD 64315 is composed of at
least two spectroscopic binaries, one of which is an eclipsing binary. HD 64315
contains two binary systems, one of which is an eclipsing binary. The two
binaries are separated by 0.09 arcsec (or 500 AU) if the most likely distance
to the system, around 5 kpc, is considered. The presence of fainter companions
is not excluded by current observations. The non-eclipsing binary (HD 64315
AaAb) has a period of 2.70962901+/-0.00000021 d. Its components are hotter than
those of the eclipsing binary, and dominate the appearance of the system. The
eclipsing binary (HD 64315 BaBb) has a shorter period of 1.0189569+/-0.0000008
d. We derive masses of 14.6+-2.3 M for both components of the BaBb
system. They are almost identical; both stars are overfilling their respective
Roche lobes, and share a common envelope in an overcontact configuration. The
non-eclipsing binary is a detached system composed of two stars with spectral
types around O6 V with minimum masses of 10.8 M and 10.2 M, and
likely masses aprox. 30 M. HD 64315 provides a cautionary tale about
high-mass star isolation and multiplicity. Its total mass is likely above 90
M,but it seems to have formed without an accompanying cluster. It
contains one the most massive overcontact binaries known, a likely merger
progenitor in a very wide multiple system.Comment: 14 pages, 13 figures, 8 Table
A comprehensive study of Cepheid variables in the Andromeda galaxy. Period distribution, blending and distance determination
Extragalactic Cepheids are the basic rungs of the cosmic distance scale. They
are excellent standard candles, although their luminosities and corresponding
distance estimates can be affected by the particular properties of the host
galaxy. Therefore, the accurate analysis of the Cepheid population in other
galaxies, and notably in the Andromeda Galaxy (M31), is crucial to obtaining
reliable distance determinations. We obtained accurate photometry (in B and V
passbands) of 416 Cepheids in M31 over a five year campaign within a survey
aimed at the detection of eclipsing binaries. The resulting Cepheid sample is
the most complete in M31 and has almost the same period distribution as the
David Dunlap Observatory sample in the Milky Way. The large number of epochs
(~250 per filter) has permitted the characterisation of the pulsation modes of
356 Cepheids, with 281 of them pulsating in the fundamental mode and 75 in the
first overtone. The period-luminosity relationship of the fundamental mode
Cepheids has been studied and a new approach has been used to estimate the
effect of blending. We find that the blending contribution is as important as
the metallicity correction when computing Cepheid distance determinations to
M31 (~0.1 mag). Since large amplitude Cepheids are less affected by blending,
we have used those with an amplitude A_V>0.8 mag to derive a distance to M31 of
(m-M)_0=24.32+/-0.12 mag.Comment: 10 pages, 9 figures; accepted for publication in A&
A new and simple variable-angle accessory for infrared specular reflectance
A simple, low-cost accessory (patent pending) with only two flat mirrors and a new variable-angle mechanism has been developed for infrared specular reflectance measurements. The system allows the angles of incidence to be varied continuously from 15° (near normal incidence) to 85° (near grazing angle) without losing the alignment of the accessory. The reflectivity of boron nitride thin films deposited on metallic substrates has been measured at different angles of incidence to demonstrate the utility of this accessory
DNA structure directs positioning of the mitochondrial genome packaging protein Abf2p
The mitochondrial genome (mtDNA) is assembled into nucleo-protein structures termed nucleoids and maintained differently compared to nuclear DNA, the involved molecular basis remaining poorly understood. In yeast (Saccharomyces cerevisiae), mtDNA is a similar to 80 kbp linear molecule and Abf2p, a double HMG-box protein, packages and maintains it. The protein binds DNA in a non-sequence-specific manner, but displays a distinct 'phased-binding' at specific DNA sequences containing poly-adenine tracts (A-tracts). We present here two crystal structures of Abf2p in complex with mtDNA-derived fragments bearing A-tracts. Each HMG-box of Abf2p induces a 90. bend in the contacted DNA, causing an overall U-turn. Together with previous data, this suggests that U-turn formation is the universal mechanism underlying mtDNA compaction induced by HMG-box proteins. Combining this structural information with mutational, biophysical and computational analyses, we reveal a unique DNA binding mechanism for Abf2p where a characteristic N-terminal flag and helix are crucial for mtDNA maintenance. Additionally, we provide the molecular basis for A-tract mediated exclusion of Abf2p binding. Due to high prevalence of Atracts in yeast mtDNA, this has critical relevance for nucleoid architecture. Therefore, an unprecedented A-tract mediated protein positioning mechanism regulates DNA packaging proteins in the mitochondria, and in combination with DNA-bending and U-turn formation, governs mtDNA compaction
Discovery of Extended Main Sequence Turnoffs in Galactic Open Clusters
The color-magnitude diagrams (CMDs) of Galactic open clusters are widely considered to be the prototypes of single stellar populations. By using photometry in ultraviolet and optical bands we discovered that the nearby young cluster NGC 6705 (M11) exhibits an extended main-sequence turnoff (eMSTO) and a broadened main sequence (MS). This is the first evidence of multiple stellar populations in a Galactic open cluster. By using high-resolution Very Large Telescope (VLT) spectra we provide direct evidence that the multiple sequences along the CMD correspond to stellar populations with different rotation rates. Specifically, the blue MS (bMS) is formed of slow-rotating stars, while red-MS (rMS) stars are fast rotators. Moreover, we exploit photometry from Gaia data release 2 (DR2) to show that three Galactic open clusters, namely NGC 2099, NGC 2360, and NGC 2818, exhibit the eMSTO, thus suggesting that it is a common feature among these objects. Our previous work on the Large Magellanic Cloud star cluster NGC 1818 shows that slowly and rapidly rotating stars populate the bMS and rMS observed in its CMD. The similarities between M11 and the young clusters of the Magellanic Clouds (MCs) suggest that rotation is responsible for the appearance of multiple populations in the CMDs of both Milky Way open clusters and MCs young clusters.A.F.M.
and L.C. acknowledge support by the Australian Research
Council through Discovery Early Career Researcher Award
DE160100851 and the Future Fellowship FT160100402.
A.P.M. has been supported by the European Research Council
through the Starting Grant “GALFOR” (716082) and the FAREMIUR project R164RM93XW “SEMPLICE”. A.S., L.B.N., and
F.V. are partially supported by the MINECO (Spanish Ministry of
Economy) through grants ESP2017-82674-R and ESP2016-
80079-C2-1-R (MINECO/FEDER, UE), SGR-1131 (Generalitat
Catalunya), and MDM-2014-0369 of ICCUB (Unidad de
Excelencia “MarĂa de Maeztu”)
Eclipsing binaries suitable for distance determination in the Andromeda galaxy
The Local Group galaxies constitute a fundamental step in the definition of
cosmic distance scale. Therefore, obtaining accurate distance determinations to
the galaxies in the Local Group, and notably to the Andromeda Galaxy (M31), is
essential to determining the age and evolution of the Universe. With this
ultimate goal in mind, we started a project to use eclipsing binaries as
distance indicators to M31. Eclipsing binaries have been proved to yield direct
and precise distances that are essentially assumption free. To do so,
high-quality photometric and spectroscopic data are needed. As a first step in
the project, broad band photometry (in Johnson B and V) has been obtained in a
region (34'x34') at the North-Eastern quadrant of the galaxy over 5 years. The
data, containing more than 250 observations per filter, have been reduced by
means of the so-called difference image analysis technique and the DAOPHOT
program. A catalog with 236238 objects with photometry in both B and V
passbands has been obtained. The catalog is the deepest (V<25.5 mag) obtained
so far in the studied region and contains 3964 identified variable stars, with
437 eclipsing binaries and 416 Cepheids. The most suitable eclipsing binary
candidates for distance determination have been selected according to their
brightness and from the modelling of the obtained light curves. The resulting
sample includes 24 targets with photometric errors around 0.01 mag. Detailed
analysis (including spectroscopy) of some 5-10 of these eclipsing systems
should result in a distance determination to M31 with a relative uncertainty of
2-3% and essentially free from systematic errors, thus representing the most
accurate and reliable determination to date.Comment: 12 pages, 9 figures; accepted for publication in A&A; see electronic
tables and full resolution images at
http://www.am.ub.es/~fvilarde/download/A+A
The eclipsing, double-lined, Of supergiant binary Cyg OB2-B17
Massive, eclipsing, double-lined, spectroscopic binaries are not common but
are necessary to understand the evolution of massive stars as they are the only
direct way to determine stellar masses. They are also the progenitors of
energetic phenomena such as X-ray binaries and gamma-ray bursts. We present a
photometric and spectroscopic analysis of the candidate binary system Cyg
OB2-B17 to show that it is indeed a massive evolved binary. We utilise V band
and white-light photometry to obtain a light curve and period of the system,
and spectra at different resolutions to calculate preliminary orbital
parameters and spectral classes for the components. Our results suggest that
B17 is an eclipsing, double-lined, spectroscopic binary with a period of
4.0217+/-0.0004 days, with two massive evolved components with preliminary
classifications of O7 and O9 supergiants. The radial velocity and light curves
are consistent with a massive binary containing components with similar
luminosities, and in turn with the preliminary spectral types and age of the
association.Comment: 10 pages, 10 figures (1 degraded), accepted for publication in
Astronomy and Astrophysic
VLT multi-object spectroscopy of 33 eclipsing binaries in the Small Magellanic Cloud. New distance and depth of the SMC, and a record-breaking apsidal motion
Aim: Our purpose is to provide reliable stellar parameters for a significant
sample of eclipsing binaries, which are representative of a whole dwarf and
metal-poor galaxy. We also aim at providing a new estimate of the mean distance
to the SMC and of its depth along the line of sight for the observed field of
view. Method: We use radial velocity curves obtained with the ESO FLAMES
facility at the VLT and light curves from the OGLE-II photometric survey. The
radial velocities were obtained by least-squares fits of the observed spectra
to synthetic ones, excluding the hydrogen Balmer lines. Results: Our sample
contains 23 detached, 9 semi-detached and 1 overcontact systems. Most detached
systems have properties consistent with stellar evolution calculations from
single-star models at the standard SMC metallicity Z = 0.004, though they tend
to be slightly overluminous. The few exceptions are probably due to third light
contribution or insufficient signal-to-noise ratio. The mass ratios are
consistent with a flat distribution, both for detached and
semi-detached/contact binaries. A mass-luminosity relation valid from ~4 to ~18
Msol is derived. The uncertainties are in the +-2 to +-11% range for the
masses, in the +-2 to +-5% range for the radii and in the +-1 to +-6% range for
the effective temperatures. The average distance modulus is 19.11+-0.03
(66.4+-0.9 kpc). The moduli derived from the V and from the I data are
consistent within 0.01 mag. The 2-sigma depth of the SMC is, for our field, of
0.25 mag or 7.6 kpc under the assumption of a gaussian distribution of stars
along the line of sight. Three systems show significant apsidal motion, one of
them with an apsidal period of 7.6 years, the shortest known to date for a
detached system with main sequence stars.Comment: 61 pages, 41 figures; accepted for publication in Astronomy &
Astrophysic
The young open cluster NGC 7067 using Strömgren photometry
© 2016 The Authors. NGC 7067 is a young open cluster located in the direction between the first and the second Galactic quadrants and close to the Perseus spiral arm. This makes it useful for studies of the nature of the MilkyWay spiral arms. Strömgren photometry taken with theWide Field Camera at the Isaac Newton Telescope allowed us to compute individual physical parameters for the observed stars and hence to derive the cluster's physical parameters. Spectra from the 1.93-m telescope at the Observatoire de Haute-Provence helped to check and improve the results. We obtained photometry for 1233 stars, individual physical parameters for 515 and spectra for 9 of them. The 139 selected cluster members lead to a cluster distance of 4.4 ±0.4 kpc, with an age below log10(t(yr)) = 7.3 and a present mass of 1260 ± 160 M⊙. The morphology of the data reveals that the centre of the cluster is at (α, δ) = (21: 24: 13.69, +48: 00: 39.2) J2000, with a radius of 6.1 arcmin. Strömgren and spectroscopic data allowed us to improve the previous parameters available for the cluster in the literature
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