3,591 research outputs found
A systematic search for novae in M31 on a large set of digitized archival Schmidt plates
This paper reports on the detection of optical novae in our neighbour galaxy
M31 based on digitized historical Tautenburg Schmidt plates. The accurate
positions of the detected novae lead to a much larger database when searching
for recurrent novae in M31. We conducted a systematic search for novae on 306
digitized Tautenburg Schmidt plates covering a time span of 36 years from 1960
to 1996. From the database of both ~ 300 000 light curves and about one million
detections on only one plate per colour band, nova candidates were efficiently
selected by automated algorithms and subsequently individually inspected by
eye. We report the detection of 84 nova candidates. We found 55 nova candidates
from the automated analysis of the light curves. Among these, 22 were
previously unknown, 12 were known but not identified on Tautenburg Schmidt
plates before, and 21 novae had been previously discovered on Tautenburg
plates. An additional 29 known novae could be confirmed by the detailed
investigation of single detections. One of our newly discovered nova candidates
shows a high position coincidence with a nova detected about 30 years earlier.
Therefore, this object is likely to be a recurrent nova. Furthermore, we
re-investigated all 41 nova candidates previously found on Tautenburg plates
and confirm all but two. Positions are given for all nova candidates with a
typical accuracy of ~ 0.4 arcsec. We present light curves and finding charts as
online material. The analysis of the plates has shown the wealth of information
still buried in old plate archives. Extrapolating from this survey,
digitization of other historical M31 plate archives (e.g. from the Mount Wilson
or Asiago observatories) for a systematic nova search looks very promising.Comment: 29 pages, 14 figures, 19 tables, accepted for publication in A&A.
Figs 6-14 are reduced in resolution due to the restrictions on space
available on astro-ph; v2: minor grammatical change
Time variability of X-ray sources in the M 31 centre field
We present an extension to our XMM-Newton X-ray source catalogue of M 31,
containing 39 newly found sources. In order to classify and identify more of
the sources we search for X-ray time variability in XMM-Newton archival data of
the M 31 centre field.
As a source list we used our extended catalogue based on observations
covering the time span from June 2000 to July 2004. We then determined the flux
or at least an upper limit at the source positions for each observation.
Deriving the flux ratios for the different observations and searching for the
maximum flux difference we determined variability factors. We also calculated
the significance of the flux ratios.
Using hardness ratios, X-ray variability and cross correlations with
catalogues in the X-ray, optical, infrared and radio regimes, we detected three
super soft source candidates, one supernova remnant and six supernova remnant
candidates, one globular cluster candidate, three X-ray binaries and four X-ray
binary candidates. Additionally we identified one foreground star candidate and
classified fifteen sources with hard spectra, which may either be X-ray
binaries or Crab-like supernova remnants in M 31 or background active galactic
nuclei. The remaining five sources stay unidentified or without classification.
Based on the time variability results we suggest six sources, which were
formerly classified as "hard", to be X-ray binary candidates. The
classification of one other source (XMMM31 J004236.7+411349) as a supernova
remnant, has to be rejected due to the distinct time variability we found. We
now classify this source as a foreground star.Comment: 13 pages, 6 figures, accepted for publication in A&
A possible X-ray jet from the starburst galaxy NGC6217
Deep ROSAT PSPC and HRI observations of the nuclear starburst, UV flat
spectrum spiral NGC6217 reveal a jet-like X-ray filament extending out 2.7'
(18.8 kpc) to the SW of the galaxy. Radio images of NGC6217 show an extent in
the same direction, giving further evidence for a one-sided X-ray jet
interpretation of this feature. It's X-ray spectrum is harder than that of
NGC6217 and the luminosity in the 0.5-2.0 keV band ~1.7 E39 erg\s. We compare
our findings to parameters of other X-ray jets from other active galaxies. We
also give positions of a total of 91 X-ray sources detected in the field to a
limiting 0.5-2.0 keV flux of ~2.2E-15 erg\cm**2\s and propose optical and radio
identifications. Some of these sources have been identified in the RIXOS
program.Comment: 9 pages, 6 figures, accepted for publication in A&A a full resolution
file is available at http://www.rosat.mpe-garching.mpg.de/~wnp
Elder Law and Conflicts of Interest in the United States and Canada
This article considers the problem of conflicts of interest in elder law in the context of a larger discussion about elder law as a bounded legal subject. The problem of conflicts of interest is not particular to elder law. Conflicts, intentional and unintentional, have a special salience in this context, however. That salience is intensified by the expanded scope of elder law to include other classes of vulnerable clients, such as persons with disabilities. Despite the significance of conflicts as a real, perceived, or potential issue in this context, the issue has received relatively scant attention and discussion. This inattention to conflicts has distorted perceptions of elder law within the wider legal community, with unfortunate consequences for the development of elder law as a discrete field of practice and research. This article considers the issue of conflicts in the elder law discourse from both an American and Canadian perspective. Core practice areas for American elder law (areas not readily transportable to non-American jurisdictions) are areas in which the conflicts issue is especially prominent. From an international perspective, a perception may be created of elder law as a peculiarly American practice area, and one which is rife with real and potential conflicts that elder law practitioners-and those who would export the model-may prefer to ignore. This dynamic has frustrated the development of elder law as an international, multi-faceted, and interdisciplinary area of law. Confronting the issue of conflicts in elder law is an important first step in continuing the coherent development of elder law (perhaps within a rubric of law, policy and aging) as a bounded legal subject
X-ray monitoring of classical novae in the central region of M 31. II. Autumn and winter 2007/2008 and 2008/2009
[Abridged] Classical novae (CNe) represent the major class of supersoft X-ray
sources (SSSs) in the central region of our neighbouring galaxy M 31. We
performed a dedicated monitoring of the M 31 central region with XMM-Newton and
Chandra between Nov 2007 and Feb 2008 and between Nov 2008 and Feb 2009
respectively, in order to find SSS counterparts of CNe, determine the duration
of their SSS phase and derive physical outburst parameters. We systematically
searched our data for X-ray counterparts of CNe and determined their X-ray
light curves and spectral properties. We detected in total 17 X-ray
counterparts of CNe in M 31, only four of which were known previously. These
latter sources are still active 12.5, 11.0, 7.4 and 4.8 years after the optical
outburst. From the 17 X-ray counterparts 13 were classified as SSSs. Four novae
displayed short SSS phases (< 100 d). Based on these results and previous
studies we compiled a catalogue of all novae with SSS counterparts in M 31
known so far. We used this catalogue to derive correlations between the
following X-ray and optical nova parameters: turn-on time, turn-off time,
effective temperature (X-ray), t2 decay time and expansion velocity of the
ejected envelope (optical). Furthermore, we found a first hint for the
existence of a difference between SSS parameters of novae associated with the
stellar populations of the M 31 bulge and disk. Additionally, we conducted a
Monte Carlo Markov Chain simulation on the intrinsic fraction of novae with SSS
phase. This simulation showed that the relatively high fraction of novae
without detected SSS emission might be explained by the inevitably incomplete
coverage with X-ray observations in combination with a large fraction of novae
with short SSS states, as expected from the WD mass distribution. In order to
verify our results with an increased sample further monitoring observations are
needed.Comment: 31 pages, 23 figures, 10 tables; submitted to A&
Constraints on the Compact Object Mass in the Eclipsing HMXB XMMU J013236.7+303228 in M33
We present optical spectroscopic measurements of the eclipsing High Mass
X-ray Binary XMMU J013236.7+303228 in M33. Based on spectra taken at multiple
epochs of the 1.73d binary orbital period we determine physical as well as
orbital parameters for the donor star. We find the donor to be a B1.5IV
sub-giant with effective temperature T=22,000-23,000 K. From the luminosity,
temperature and known distance to M33 we derive a radius of R = 8.9 \pm 0.5
R_sun. From the radial--velocity measurements, we determine a velocity
semi-amplitude of K_opt = 63 \pm 12 km/sec. Using the physical properties of
the B-star determined from the optical spectrum, we estimate the star's mass to
be M_opt = 11 \pm 1 M_sun. Based on the X-ray spectrum, the compact companion
is likely a neutron star, although no pulsations have yet been detected. Using
the spectroscopically derived B-star mass we find the neutron star companion
mass to be M_X = 2.0 \pm 0.4 M_sun, consistent with the neutron star mass in
the HMXB Vela X-1, but heavier than the canonical value of 1.4 M_sun found for
many millisecond pulsars. We attempt to use as an additional constraint that
the B star radius inferred from temperature, flux, and distance, should equate
the Roche radius, since the system accretes by Roche lobe overflow. This leads
to substantially larger masses, but from trying to apply the technique to known
systems, we find that the masses are consistently overestimated. Attempting to
account for that in our uncertainties, we derive M_X = 2.2^{+0.8}_{-0.6} M_sun
and M_opt =13 \pm 4 M_sun. We conclude that precise constraints require
detailed modeling of the shape of the Roche surface.Comment: 11 pages emulateapj, 9 figures, ApJ accepte
J004457+4123 (Sharov 21): not a remarkable nova in M31 but a background quasar with a spectacular UV flare
We announce the discovery of a quasar behind the disk of M31, which was
previously classified as a remarkable nova in our neighbour galaxy. The paper
is primarily aimed at the outburst of J004457+4123 (Sharov 21), with the first
part focussed on the optical spectroscopy and the improvement in the
photometric database. Both the optical spectrum and the broad band spectral
energy distribution of Sharov 21 are shown to be very similar to that of
normal, radio-quiet type 1 quasars. We present photometric data covering more
than a century and resulting in a long-term light curve that is densely sampled
over the past five decades. The variability of the quasar is characterized by a
ground state with typical fluctuation amplitudes of ~0.2 mag around B~20.5,
superimposed by a singular flare of ~2 yr duration (observer frame) with the
maximum at 1992.81 where the UV flux has increased by a factor of ~20. The
total energy in the flare is at least three orders of magnitudes higher than
the radiated energy of the most luminous supernovae, provided that it comes
from an intrinsic process and the energy is radiated isotropically. The profile
of the flare light curve appears to be in agreement with the standard
predictions for a stellar tidal disruption event where a ~10 M_sun giant star
was shredded in the tidal field of a ~2...5 10^8 M_sun black hole. The short
fallback time derived from the light curve requires an ultra-close encounter
where the pericentre of the stellar orbit is deep within the tidal disruption
radius. Gravitational microlensing provides an alternative explanation, though
the probability of such a high amplification event is very low.Comment: Accepted for publication in Astronomy and Astrophysics, 14 pages, 11
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