112 research outputs found
Eclipsing high-mass binaries I. Light curves and system parameters for CPD-518946, PISMIS24-1 and HD319702
We present first results of a comprehensive photometric O-star survey
performed with a robotic twin refractor at the Universit\"atssternwarte Bochum
located near Cerro Armazones in Chile. For three high-mass stars, namely
Pismis24-1, CPD-518946 and HD319702, we determined the period through the
Lafler-Kinman algorithm and model the light curves within the framework of the
Roche geometry. For Pismis24-1, a previously known eclipsing binary, we provide
first light curves and determined a photometric period of 2.36 days together
with an orbital inclination of 61.8 degrees. The best-fitting model solution to
the light curves suggest a detached configuration. With a primary temperature
of T1 = 42520K we obtain the temperature of the secondary component as T2 =
41500K. CPD-518946 is another known eclipsing binary for which we present a
revised photometric period of 1.96 days with an orbital inclination of 58.4
degrees. The system has likely a semi-detached configuration and a mass ratio q
= M1/M2 = 2.8. If we adopt a primary temperature of T1 = 34550K we obtain T2 =
21500K for the secondary component. HD319702 is a newly discovered eclipsing
binary member of the young open cluster NGC6334. The system shows well-defined
eclipses favouring a detached configuration with a period of 2.0 days and an
orbital inclination of 67.5 degrees. Combining our photometric result with the
primary spectral type O8 III(f) (T1 = 34000K) we derive a temperature of T2 =
25200K for the secondary component.Comment: 7 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
An eccentric companion at the edge of the brown dwarf desert orbiting the 2.4 Msun giant star HIP67537
We report the discovery of a substellar companion around the giant star
HIP67537. Based on precision radial velocity measurements from CHIRON and FEROS
high-resolution spectroscopic data, we derived the following orbital elements
for HIP67537: msin = 11.1 M,
= 4.9 AU and = 0.59. Considering
random inclination angles, this object has 65% probability to be
above the theoretical deuterium-burning limit, thus it is one of the few known
objects in the planet to brown-dwarf transition region. In addition, we
analyzed the Hipparcos astrometric data of this star, from which we derived a
minimum inclination angle for the companion of 2 deg. This value
corresponds to an upper mass limit of 0.3 M, therefore the
probability that HIP67537 is stellar in nature is 7%. The large
mass of the host star and the high orbital eccentricity makes HIP67537 a
very interesting and rare substellar object. This is the second candidate
companion in the brown dwarf desert detected in the sample of intermediate-mass
stars targeted by the EXPRESS radial velocity program, which corresponds to a
detection fraction of = 1.6%. This value is larger than the
fraction observed in solar-type stars, providing new observational evidence of
an enhanced formation efficiency of massive substellar companions in massive
disks. Finally, we speculate about different formation channels for this
object.Comment: Accepted for publication to A&
Dust reverberation-mapping of the Seyfert 1 galaxy WPVS48
Using robotic telescopes of the Universitatssternwarte Bochum near Cerro
Armazones in Chile, we monitored the z=0.0377 Seyfert 1 galaxy WPVS48 (2MASX
J09594263-3112581) in the optical (B and R) and near-infrared (NIR, J and Ks)
with a cadence of two days. The light curves show unprecedented variability
details. The NIR variation features of WPVS48 are consistent with the
corresponding optical variations, but the features appear sharper in the NIR
than in the optical, suggesting that the optical photons undergo multiple
scatterings. The J and Ks emission, tracing the hot (1600 K) dust echo, lags
the B and R variations by on average 64 +/- 4 days and 71 +/- 5 days,
respectively (restframe). WPVS48 lies on the known tau-M_V relationship.
However, the observed lag is about three times shorter than expected from the
dust sublimation radius r_sub inferred from the optical-UV luminosity, and
explanations for this common discrepancy are searched for. The sharp NIR echos
argue for a face-on torus geometry and allow us to put forward two potential
scenarios: 1) as previously proposed, in the equatorial plane of the accretion
disk the inner region of the torus is flattened and may come closer to the
accretion disk. 2) The dust torus with inner radius r_sub is geometrically and
optically thick, so that the observer only sees the facing rim of the torus
wall, which lies closer to the observer than the torus equatorial plane and
therefore leads to an observed foreshortened lag. Both scenarios are able to
explain the factor three discrepancy between tau and r_sub. Longer-wavelength
dust reverberation data might enable one to distinguish between the scenarios.Comment: 4 pages, 6 figures, Published in Astronomy and Astrophysic
Early Dust Formation and a Massive Progenitor for SN 2011ja?
SN 2011ja was a bright (I = -18.3) Type II supernova occurring in the nearby
edge on spiral galaxy NGC 4945. Flat-topped and multi-peaked H-alpha and H-beta
spectral emission lines appear between 64 - 84 days post-explosion, indicating
interaction with a disc-like circumstellar medium inclined 30-45 degrees from
edge-on. After day 84 an increase in the H- and K-band flux along with heavy
attenuation of the red wing of the emission lines are strong indications of
early dust formation, likely located in the cool dense shell created between
the forward shock of the SN ejecta and the reverse shock created as the ejecta
plows into the existing CSM. Radiative transfer modeling reveals both ~1.5 x
10^-4 Msun of pre-existing dust located ~ 10^16.7 cm away and ~ 5 x 10^-5 Msun
of newly formed dust. Spectral observations after 1.5 years reveal the
possibility that the fading SN is located within a young (3-6 Myr) massive
stellar cluster, which when combined with tentative 56Ni mass estimates of 0.2
Msun may indicate a massive (> 25 Msun) progenitor for SN 2011ja.Comment: 13 pages, 8 figures, submitted to MNRAS awaiting final referee repor
Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars
CONTEXT. Exoplanet searches have demonstrated that giant planets are
preferentially found around metal-rich stars and that their fraction increases
with the stellar mass. AIMS. During the past six years, we have conducted a
radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this
information, we aim to study the role of the stellar evolution in the orbital
parameters of the companions, and to unveil possible correlations between the
stellar properties and the occurrence rate of giant planets. METHODS. Using
FEROS and CHIRON spectra, we have computed precision radial velocities and we
have derived atmospheric and physical parameters for all of our targets.
Additionally, velocities computed from UCLES spectra are presented here. By
studying the periodic radial velocity signals, we have detected the presence of
several substellar companions. RESULTS. We present four new planetary systems
around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we find that giant planets are more frequent around metal-rich stars, reaching
a peak in the detection of = 16.7% around stars with
[Fe/H] 0.35 dex. Similarly, we observe a positive correlation of the
planet occurrence rate with the stellar mass, between M 1.0 -2.1
M, with a maximum of = 13.0%, at M = 2.1
M. CONCLUSIONS. We conclude that giant planets are preferentially
formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the mass range of M
1.0 - 2.1 M. These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support
to the core-accretion formation model.Comment: Accepted for publication in A&
The reddest ISO-2MASS quasar
In the course of the NIR/MIR AGN search combining the 6.7 mu ISOCAM Parallel
Survey and 2MASS we have discovered 24 type-1 quasars about a third of which
are too red to be discriminated by optical/UV search techniques. Here we report
on a detailed case study of the reddest type-1 quasar of our sample (J2341) at
redshift z=0.236 with M_K=-25.8 and J-K=1.95. We performed spectroscopy in the
optical with VLT/FORS1 and in the MIR with Spitzer as well as NIR imaging with
ISPI at CTIO. The optical and NIR observations reveal a star forming
emission-line galaxy at the same redshift as the quasar with a projected linear
separation of 1.8 arcsec (6.7 kpc). The quasar and its companion are embedded
in diffuse extended continuum emission. Compared with its companion the quasar
exhibits redder optical-NIR colours, which we attribute to hot nuclear dust.
The MIR spectrum shows only few emission lines superimposed on a power-law
spectral energy distribution. However, the lack of strong FIR emission suggests
that our potentially interacting object contains much less gas and dust and is
in a stage different from dust reddened ULIRG-AGN like Mrk 231. The optical
spectrum shows signatures for reddening in the emission-lines and no
post-starburst stellar population is detected in the host galaxy of the quasar.
The optical continuum emission of the active nucleus appears absorbed and
diluted. Even the combination of absorption and host dilution is not able to
match J2341 with standard quasar templates. While the BLR shows only a rather
moderate absorption of E_(B-V)=0.3, the continuum shorter than 4500 AA requires
strong obscuration with E_(B-V)=0.7, exceeding the constraints from the low
upper limit on the 9.7 mu silicate absorption. This leads us to conclude that
the continuum of J2341 is intrinsically redder than that of typical quasars.Comment: 8 pages, 9 figure
A near-infrared survey of the entire R Corona Australis cloud
To understand low- to intermediate-mass star-formation in the nearby R CrA
molecular cloud, we try to identify the stellar content that is accessible with
near-infrared observations. We obtained a JHK band mosaic of 10 x 60 arcmin
square covering the entire RCrA molecular cloud with unprecedented sensitivity.
We present a catalogue of about 3500 near-infrared sources fainter than the
saturation limit K = 10 mag, reaching K = 18mag. We analysed the extended
sources by inspecting their morphology and point sources by means of
colour-colour and colour-magnitude diagrams. Additionally, we compared the
extinction inferred from the NIR data with the line-of-sight dust emission at
1.2 mm. Sources towards high dust emission but relatively low H-K show a
projected mm-exces; these sources are either immediately surrounded by cold
circumstellar material or, if too red to be a true foreground object, they are
embedded in the front layer of the 1.2 mm emitting dust cloud. In both cases
they are most likely associated with the cloud.Comment: 11 pages, 12 Figures, accepted by Astronomy and Astrophysic
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