127 research outputs found
Constraints on the Equation-of-State of neutron stars from nearby neutron star observations
We try to constrain the Equation-of-State (EoS) of supra-nuclear-density
matter in neutron stars (NSs) by observations of nearby NSs. There are seven
thermally emitting NSs known from X-ray and optical observations, the so-called
Magnificent Seven (M7), which are young (up to few Myrs), nearby (within a few
hundred pc), and radio-quiet with blackbody-like X-ray spectra, so that we can
observe their surfaces. As bright X-ray sources, we can determine their
rotational (pulse) period and their period derivative from X-ray timing. From
XMM and/or Chandra X-ray spectra, we can determine their temperature. With
precise astrometric observations using the Hubble Space Telescope, we can
determine their parallax (i.e. distance) and optical flux. From flux, distance,
and temperature, one can derive the emitting area - with assumptions about the
atmosphere and/or temperature distribution on the surface. This was recently
done by us for the two brightest M7 NSs RXJ1856 and RXJ0720. Then, from
identifying absorption lines in X-ray spectra, one can also try to determine
gravitational redshift. Also, from rotational phase-resolved spectroscopy, we
have for the first time determined the compactness (mass/radius) of the M7 NS
RBS1223. If also applied to RXJ1856, radius (from luminosity and temperature)
and compactness (from X-ray data) will yield the mass and radius - for the
first time for an isolated single neutron star. We will present our
observations and recent results.Comment: refereed NPA5 conference proceedings, in pres
On identifying the neutron star that was born in the supernova that placed 60Fe onto the Earth
Recently, 60Fe was found in the Earth crust formed in a nearby recent
supernova (SN). If the distance to the SN and mass of the progenitor of that SN
was known, then one could constrain SN models. Knowing the positions, proper
motions, and distances of dozens of young nearby neutron stars, we can
determine their past flight paths and possible kinematic origin. Once the birth
place of a neutron star in a SN is found, we would have determined the distance
of the SN and the mass of the SN progenitor star.Comment: refereed NPA5 conference proceedings, in pres
The Hercules-Lyra Association revisited New age estimation and multiplicity study
The Her-Lyr assoc., a nearby young MG, contains a few tens of ZAMS stars of
SpT F to M. The existence and the properties of the Her-Lyr assoc. are
controversial and discussed in the literature. The present work reassesses
properties and the member list of Her-Lyr assoc., based on kinematics and age.
Many objects form multiple systems or have low-mass companions and so we need
to account for multiplicity. We use our own new imaging obs. and archival data
to identify multiple systems. The colors and magnitudes of kinematic candidates
are compared to isochrones. We derive further information on the age based on
Li depletion, rotation, and coronal and chromospheric activity. A set of
canonical members is identified to infer mean properties. Membership criteria
are derived from the mean properties and used to discard non-members. The
candidates selected from the literature belong to 35 stellar systems, 42.9% of
which are multiple. Four multiple systems are confirmed in this work by common
proper motion. An orbital solution is presented for the binary system HH Leo B
and C. Indeed, a group of candidates displays signatures of youth. 7 canonical
members are identified. The distribution of EWLi of canonical Her-Lyr members
is spread widely and is similar to that of the Pleiades and the UMa group.
Gyrochronology gives an age of 257+-46 Myr which is in between the ages of the
Pleiades and the Ursa Major group. The measures of chromospheric and coronal
activity support the young age. Four membership criteria are presented based on
kinematics, EWLi, chromospheric activity, and gyro. age. In total, 11 stars are
identified as certain members including co-moving objects plus additional 23
possible members while 14 candidates are doubtful or can be rejected. A
comparison to the mass function, however, indicates the presence of a large
number of additional unidentified low-mass members.Comment: 19 pages 16 figure
Transit observations at the observatory in Grossschwabhausen: XO-1b and TrES-1
We report on observations of transit events of the transiting planets XO-1b
and TrES-1 with the AIU Jena telescope in Grossschwabhausen. Based on our IR
photometry (in March 2007) and available transit timings (SuperWASP, XO and
TLC-project-data) we improved the orbital period of XO-1b (P =
3.9414970.000006) and TrES-1 (P = 3.03007370.000006), respectively.
The new ephemeris for the both systems are presented.Comment: 4 pages, 2 figure
Variability of young stars: Determination of rotational periods of weak-line T Tauri stars in the Cepheus-Cassiopeia star-forming region
We report on observation and determination of rotational periods of ten
weak-line T Tauri stars in the Cepheus-Cassiopeia star-forming region.
Observations were carried out with the Cassegrain-Teleskop-Kamera (CTK) at
University Observatory Jena between 2007 June and 2008 May. The periods
obtained range between 0.49 d and 5.7 d, typical for weak-line and post T Tauri
stars.Comment: 11 pages, 26 figures, accepted to be published in A
WASP-14 b: Transit Timing analysis of 19 light curves
Although WASP-14 b is one of the most massive and densest exoplanets on a
tight and eccentric orbit, it has never been a target of photometric follow-up
monitoring or dedicated observing campaigns. We report on new photometric
transit observations of WASP-14 b obtained within the framework of "Transit
Timing Variations @ Young Exoplanet Transit Initiative" (TTV@YETI). We
collected 19 light-curves of 13 individual transit events using six telescopes
located in five observatories distributed in Europe and Asia. From light curve
modelling, we determined the planetary, stellar, and geometrical properties of
the system and found them in agreement with the values from the discovery
paper. A test of the robustness of the transit times revealed that in case of a
non-reproducible transit shape the uncertainties may be underestimated even
with a wavelet-based error estimation methods. For the timing analysis we
included two publicly available transit times from 2007 and 2009. The long
observation period of seven years (2007-2013) allowed us to refine the transit
ephemeris. We derived an orbital period 1.2 s longer and 10 times more precise
than the one given in the discovery paper. We found no significant periodic
signal in the timing-residuals and, hence, no evidence for TTV in the system.Comment: 12 pages, 10 figures, 7 table
Towards the Rosetta Stone of planet formation
Transiting exoplanets (TEPs) observed just about 10 Myrs after formation of
their host systems may serve as the Rosetta Stone for planet formation
theories. They would give strong constraints on several aspects of planet
formation, e.g. time-scales (planet formation would then be possible within 10
Myrs), the radius of the planet could indicate whether planets form by
gravitational collapse (being larger when young) or accretion growth (being
smaller when young). We present a survey, the main goal of which is to find and
then characterise TEPs in very young open clusters.Comment: Poster contribution to Detection and Dynamics of Transiting
Exoplanets (Haute Provence Observatory Colloquium, 23-27 August 2010
Transit observation at the observatory in Großschwabhausen: XO-1b and TrES-1
We report on observations of transit events of the transiting planets XO-1b and TrES-1 with the AIU Jena telescope in Großschwabhausen. Based on our (IR) photometry (in March 2007) and available transit timings (SuperWASP, XO and TLC-project-data) we improved the orbital period of XO-1b (P = 3.941497 ± 0.000006) and TrES-1 (P = 3.0300737 ± 0.000006), respectively. The new ephemeris for the both systems are presente
A lucky imaging multiplicity study of exoplanet host stars
To understand the influence of additional wide stellar companions on planet
formation, it is necessary to determine the fraction of multiple stellar
systems amongst the known extrasolar planet population. We target recently
discovered radial velocity exoplanetary systems observable from the northern
hemisphere and with sufficiently high proper motion to detect stellar
companions via direct imaging. We utilize the Calar Alto 2.2m telescope in
combination with its lucky imaging camera AstraLux. 71 planet host stars have
been observed so far, yielding one new low-mass (0.239 \pm 0.022M\odot) stellar
companion, 4.5 arcsec (227AU of projected separation) northeast of the planet
host star HD185269, detected via astrometry with AstraLux. We also present
follow-up astrometry on three previously discovered stellar companions, showing
for the first time common proper motion of the 0.5 arcsec companion to
HD126614. Additionally, we determined the achieved detection limits for all
targets, which allows us to characterize the detection space of possible
further companions of these stars
Observations of the transiting planet TrES-2 with the AIU Jena telescope in Großschwabhausen
We have started high precision photometric monitoring observations at the AIU Jena observatory in Großschwabhausen near Jena in fall 2006. We used a 25.4cm Cassegrain telescope equipped with a CCD-camera mounted piggyback on a 90cm telescope. To test the attainable photometric precision, we observed stars with known transiting planets. We could recover all planetary transits observed by us. We observed the parent star of the transiting planet TrES-2 over a longer period in Großschwabhausen. Between March and November 2007 seven different transits and almost a complete orbital period were analyzed. Overall, in 31 nights of observation 3423 exposures (in total 57.05h of observation) of the TrES-2 parent star were taken. Here, we present our methods and the resulting light curves. Using our observations we could improve the orbital parameters of the syste
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