240 research outputs found
The outer regions of the giant Virgo galaxy M87. Kinematic separation of stellar halo and intracluster light
We present a spectroscopic study of 287 Planetary Nebulas (PNs) in a total
area of ~0.4 deg^2 around the BCG M87 in Virgo A. With these data we can
distinguish the stellar halo from the co-spatial intracluster light (ICL). PNs
were identified from their narrow and symmetric redshifted lambda 5007\4959
Angstrom [OIII] emission lines, and the absence of significant continuum. We
implement a robust technique to measure the halo velocity dispersion from the
projected phase-space to identify PNs associated with the M87 halo and ICL. The
velocity distribution of the spectroscopically confirmed PNs is bimodal,
containing a narrow component centred on the systemic velocity of the BCG and
an off-centred broader component, that we identify as halo and ICL,
respectively. Halo and ICPN have different spatial distributions: the halo PNs
follow the galaxy's light, whereas the ICPNs are characterised by a shallower
power-law profile. The composite PN number density profile shows the
superposition of different PN populations associated with the M87 halo and the
ICL, characterised by different PN alpha-parameters, the ICL contributing ~3
times more PNs per unit light. Down to m_5007=28.8, the M87 halo PN luminosity
function (PNLF) has a steeper slope towards faint magnitudes than the IC PNLF,
and both are steeper than the standard PNLF for the M31 bulge. Moreover, the IC
PNLF has a dip at ~1-1.5 mag fainter than the bright cutoff, reminiscent of the
PNLFs of systems with extended star formation history. The M87 halo and the
Virgo ICL are dynamically distinct components with different density profiles
and velocity distribution. The different alpha values and PNLF shapes of the
halo and ICL indicate distinct parent stellar populations, consistent with the
existence of a gradient towards bluer colours at large radii. These results
reflect the hierarchical build-up of the Virgo cluster.Comment: 16 pages, 13 figures, 3 tables, A&A, in pres
On the nature of the hard X-ray source 4U2206+54
The recent discovery of a ~9.5-d period in the X-ray lightcurve of the
massive X-ray binary 4U2206+54 has opened the possibility that it is a Be/X-ray
binary with an unusually close orbit, which, together with its low intrinsic
luminosity, suggests that the system is actually a Be + WD binary, in which a
white dwarf accretes material from the dense circumstellar disc surrounding a
classical Be star. In this paper we present new X-ray observations and for the
first time high-resolution optical spectroscopy of the source. We show that
both the X-ray behaviour and the characteristics of the optical counterpart, BD
+53 2790, are more consistent with a neutron star accreting from the wind of an
early-type star. The X-ray lightcurve shows irregular flaring and no
indications of pulsations, while the very high hydrogen column density supports
accretion from a dense wind. BD +53 2790 is shown not to be a classical Be
star, as believed until now, but rather a very peculiar late O-type active
star, exhibiting emission components in the HeII lines, complex spectral
variability and strong wind resonance lines in the ultraviolet. Though many of
the characteristics of the spectrum resemble those of the He-rich stars, the
absence of HeI variability makes a connection unlikely. The spectrum is
compatible with a composite of two stars of similar spectral type, though
circumstantial evidence points to a single very peculiar active early-type
star. This adds weight to the growing evidence that the traditional
subdivisions of supergiant and Be/X-ray binaries fail to cover the whole
phenomenology of massive X-ray binaries.Comment: 10 pages, 7 figures, uses new aa.cls; accepted for publication in A&
Comparison of the Hα circumstellar disks in Be/X-ray binaries and Be stars
We present a comparative study of the circumstellar disks in Be/X-ray binaries and isolated Be stars based upon the Hα emission line. From this comparison it follows that the overall structure of the disks in the Be/X-ray binaries is similar to the disks of other Be stars, i.e. they are axisymmetric and rotationally supported. The factors for the line broadening (rotation and temperature) in the disks of the Be stars and the Be/X-ray binaries seem to be identical. However, we do detect some intriguing differences between the envelopes. On average, the circumstellar disks of the Be/X-ray binaries are twice as dense as the disks of the isolated Be stars. The different distribution of the Be/X-ray binaries and the Be stars seen in the full with half maximum versus peak separation diagram indicates that the disks in Be/X-ray binaries have on average a smaller size, probably truncated by the compact object.Reig Torres, Pablo, [email protected] ; Fabregat Llueca, Juan, [email protected]
The Astro-WISE approach to quality control for astronomical data
We present a novel approach to quality control during the processing of
astronomical data. Quality control in the Astro-WISE Information System is
integral to all aspects of data handing and provides transparent access to
quality estimators for all stages of data reduction from the raw image to the
final catalog. The implementation of quality control mechanisms relies on the
core features in this Astro-WISE Environment (AWE): an object-oriented
framework, full data lineage, and both forward and backward chaining. Quality
control information can be accessed via the command-line awe-prompt and the
web-based Quality-WISE service. The quality control system is described and
qualified using archive data from the 8-CCD Wide Field Imager (WFI) instrument
(http://www.eso.org/lasilla/instruments/wfi/) on the 2.2-m MPG/ESO telescope at
La Silla and (pre-)survey data from the 32-CCD OmegaCAM instrument
(http://www.astro-wise.org/~omegacam/) on the VST telescope at Paranal.Comment: Accepted for publication in topical issue of Experimental Astronomy
on Astro-WISE information syste
A study of the B and Be star population in the field of the LMC open cluster NGC2004 with VLT-FLAMES
Observations of hot stars belonging to the young cluster LMC-NGC2004 and its
surrounding region have been obtained with the VLT-GIRAFFE facilities in MEDUSA
mode. 25 Be stars were discovered; the proportion of Be stars compared to
B-type stars is found to be of the same order in the LMC and in the Galaxy
fields. 23 hot stars were discovered as spectroscopic binaries (SB1 and SB2), 5
of these are found to be eclipsing systems from the MACHO database, with
periods of a few days. About 75% of the spectra in our sample are polluted by
hydrogen (Halpha and Hgamma), [SII] and [NII] nebular lines. These lines are
typical of HII regions. They could be associated with patchy nebulosities with
a bi-modal distribution in radial velocity, with higher values (+335 kms^{-1})
preferentially seen inside the southern part of the known bubble LMC4 observed
in HI at 21 cm.Comment: 12 pages, 17 figures, accepted to A&
Properties and nature of Be stars: 27. Orbital and recent long-term variations of the Pleiades Be star Pleione = BU Tauri
Radial-velocity variations of the H-alpha emission measured on the steep
wings of the H-alpha line, prewhitened for the long-time changes, vary
periodically with a period of (218.025 +/- 0.022)d, confirming the suspected
binary nature of the bright Be star Pleione, a member of the Pleiades cluster.
The orbit seems to have a high eccentricity over 0.7, but we also briefly
discuss the possibility that the true orbit is circular and that the
eccentricity is spurious owing to the phase-dependent effects of the
circumstellar matter. The projected angular separation of the spectroscopic
orbit is large enough to allow the detection of the binary with large optical
interferometers, provided the magnitude difference primary - secondary is not
too large. Since our data cover the onset of a new shell phase up to
development of a metallic shell spectrum, we also briefly discuss the recent
long-term changes. We confirm the formation of a new envelope, coexisting with
the previous one, at the onset of the new shell phase. We find that the full
width at half maximum of the H-alpha profile has been decreasing with time for
both envelopes. In this connection, we briefly discuss Hirata's hypothesis of
precessing gaseous disk and possible alternative scenarios of the observed
long-term changes
A representative sample of Be stars III: H band spectroscopy
We present H band (1.53 - 1.69 micron) spectra of 57 isolated Be stars of
spectral types O9-B9 and luminosity classes III,IV & V. The HI Brackett (n-4)
series is seen in emission from Br 11-18, and FeII emission is also apparent
for a subset of those stars with HI emission. No emission from species with a
higher excitation temperature, such as He II or CIII is seen, and no forbidden
line emission is present. A subset of 12 stars show no evidence for emission
from any species; these stars appear indistinguishable from normal B stars of a
comparable spectral type. In general the line ratios constructed from the
transitions in the range Br 11-18 do not fit case B recombination theory
particularly well. Strong correlations between the line ratios with Br-gamma
and spectral type are found. These results most likely represent systematic
variations in the temperature and ionization of the circumstellar disc with
spectral type. Weak correlations between the line widths and projected
rotational velocity of the stars are observed; however no systematic trend for
increasing line width through the Brackett series is observed.Comment: accepted for publication in A&A (this version correctly formatted
3D simulations of Rayleigh-Taylor mixing in core-collapse SNe with CASTRO
We present multidimensional simulations of the post-explosion hydrodynamics
in three different 15 solar mass supernova models with zero, 10^{-4} solar
metallicity, and solar metallicities. We follow the growth of the
Rayleigh-Taylor instability that mixes together the stellar layers in the wake
of the explosion. Models are initialized with spherically symmetric explosions
and perturbations are seeded by the grid. Calculations are performed in
two-dimensional axisymmetric and three-dimensional Cartesian coordinates using
the new Eulerian hydrodynamics code, CASTRO. We find as in previous work, that
Rayleigh-Taylor perturbations initially grow faster in 3D than in 2D. As the
Rayleigh-Taylor fingers interact with one another, mixing proceeds to a greater
degree in 3D than in 2D, reducing the local Atwood number and slowing the
growth rate of the instability in 3D relative to 2D. By the time mixing has
stopped, the width of the mixed region is similar in 2D and 3D simulations
provided the Rayleigh-Taylor fingers show significant interaction. Our results
imply that 2D simulations of light curves and nucleosynthesis in supernovae
(SNe) that die as red giants may capture the features of an initially
spherically symmetric explosion in far less computational time than required by
a full 3D simulation. However, capturing large departures from spherical
symmetry requires a significantly perturbed explosion. Large scale asymmetries
cannot develop through an inverse cascade of merging Rayleigh-Taylor
structures; they must arise from asymmetries in the initial explosion.Comment: 12 pages, 5 figures, ApJ accepte
Discovery of a Transition to Global Spin-up in EXO 2030+375
EXO 2030+375, a 42-second transient X-ray pulsar with a Be star companion,
has been observed to undergo an outburst at nearly every periastron passage for
the last 13.5 years. From 1994 through 2002, the global trend in the pulsar
spin frequency was spin-down. Using RXTE data from 2003 September, we have
observed a transition to global spin-up in EXO 2030+375. Although the spin
frequency observations are sparse, the relative spin-up between 2002 June and
2003 September observations, along with an overall brightening of the outbursts
since mid 2002 observed with the RXTE ASM, accompanied by an increase in
density of the Be disk, indicated by infrared magnitudes, suggest that the
pattern observed with BATSE of a roughly constant spin frequency, followed by
spin-up, followed by spin-down is repeating. If so this pattern has
approximately an 11 year period, similar to the 15 +/- 3 year period derived by
Wilson et al. (2002) for the precession period of a one-armed oscillation in
the Be disk. If this pattern is indeed repeating, we predict a transition from
spin-up to spin-down in 2005.Comment: Accepted for publication in ApJ Letters, 4 pages, 5 figures, using
emulateapj.cl
Simply Swivel Seat - Assistive Device
Poster is of the Simply Swivel Seat - Assistive Device that allows you to sit while entering and exiting the bathtub safely. The seat sits over the edge of the tub and rotates as you lift your legs into or out of the bathtub. The device provides support and minimizes the fear of falling.https://jdc.jefferson.edu/id/1001/thumbnail.jp
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