2,068 research outputs found
Surveyor spacecraft system - Surveyor 6 flight performance Final report
Surveyor 6 spacecraft flight performance characteristics, including data on television equipment, alpha scattering experiment, and powered flight translatio
On the mass of the neutron star in Cyg X-2
We present new high resolution spectroscopy of the low mass X-ray binary Cyg
X-2 which enables us to refine the orbital solution and rotational broadening
of the donor star. In contrast with Elebert et al (2009) we find a good
agreement with results reported in Casares et al. (1998). We measure
day, km s and km s. These values imply and
M (for ). Therefore, the
neutron star in Cyg X-2 can be more massive than canonical. We also find no
evidence for irradiation effects in our radial velocity curve which could
explain the discrepancy between Elebert et al's and our values.Comment: Accepted for publication in MNRA
The evolution of the high energy tail in the quiescent spectrum of the soft X-ray transient Aql X-1
A moderate level of variability has been detected in the quiescent luminosity
of several neutron star soft X-ray transients. Spectral variability was first
revealed by Chandra observations of Aql X-1 in the four months that followed
the 2000 X-ray outburst. By adopting the canonical model for quiescent spectrum
of soft X-ray transients, i.e. an absorbed neutron star atmosphere model plus a
power law tail, Rutledge et al. (2002a) concluded that the observed spectral
variations can be ascribed to temperature variations of the neutron star
atmosphere. These results can hardly be reconciled with the neutron star
cooling that is expected to take place in between outbursts (after deep crustal
heating in the accretion phase). Here we reanalyse the Chandra spectra of Aql
X-1, together with a long BeppoSAX observation in the same period, and propose
a different interpretation of the spectral variability: that this is due to
correlated variations of the power law component and the column density (>5, a
part of which might be intrinsic to the source), while the temperature and flux
of the neutron star atmospheric component remained unchanged. This lends
support to the idea that the power law component arises from emission at the
shock between a radio pulsar wind and inflowing matter from the companion star.Comment: 6 pages, 2 figures. Accepted for publication on Ap
Dale Goble as a Builder of Bridges
Ecological scientists and legal scholars think and talk in different ways. The âgulf of mutual incomprehensionâ that results can impede efforts to address shared problems. Dale Goble bridged this gulf by teaming with ecologists to interpret the Endangered Species Act and develop the concept of conservation-reliant speciesâspecies that require ongoing, long-term management to address the factors that threaten them. Most imperiled species are conservation reliant and conservation resources are limited. Meeting the long-term needs of conservation-reliant species will require the blending of ecological science, societal context, and law that Dale Goble has long promoted
H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks
We present detections of numerous 10-20 micron H2O emission lines from two
protoplanetary disks around the T Tauri stars AS 205A and DR Tau, obtained
using the InfraRed Spectrograph on the Spitzer Space Telescope. Follow-up 3-5
micron Keck-NIRSPEC data confirm the presence of abundant water and spectrally
resolve the lines. We also detect the P4.5 (2.934 micron) and P9.5 (3.179
micron) doublets of OH and 12CO/13CO v=1-0 emission in both sources. Line
shapes and LTE models suggest that the emission from all three molecules
originates between ~0.5 and 5 AU, and so will provide a new window for
understanding the chemical environment during terrestrial planet formation. LTE
models also imply significant columns of H2O and OH in the inner disk
atmospheres, suggesting physical transport of volatile ices either vertically
or radially; while the significant radial extent of the emission stresses the
importance of a more complete understanding of non-thermal excitation
processes.Comment: 9 pages, 3 figures, 1 table, aastex, to appear in the Astrophysical
Journa
T Pyxidis: The First Cataclysmic Variable with a Collimated Jet
We present the first observational evidence for a collimated jet in a
cataclysmic variable system; the recurrent nova T Pyxidis. Optical spectra show
bipolar components of H with velocities , very similar
to those observed in the supersoft X-ray sources and in SS 433. We argue that a
key ingredient of the formation of jets in the supersoft X-ray sources and T
Pyx (in addition to an accretion disk threaded by a vertical magnetic field),
is the presence of nuclear burning on the surface of the white dwarf.Comment: 10 pages 2 figures to appear in ApJ Letter
Tarwe bijvoeren aan vleeskuikens financieel aantrekkelijk!
Op basis van de technische resultaten van de proeven waarin tarwe is bijgevoerd aan vleeskuikens (zie pag. 21-26) is een economische evaluatie uitgevoerd. Hieruit blijkt dat bij de huidige prijsverhoudingen van de verschillende voeders het bijvoeren van tarwe financieel aantrekkelijk is
A Radial Velocity Study of CTCV J1300-3052
We present time-resolved spectroscopy of the eclipsing, short period
cataclysmic variable CTCV J1300-3052. Using absorption features from the
secondary star, we determine the radial velocity semi-amplitude of the
secondary star to be K2 = 378 \pm 6 km/s, and its projected rotational velocity
to be v sin i = 125 \pm 7 km/s. Using these parameters and Monte Carlo
techniques, we obtain masses of M1 = 0.79 \pm 0.05 MSun for the white dwarf
primary and M2 = 0.198 \pm 0.029 MSun for the M-type secondary star. These
parameters are found to be in excellent agreement with previous mass
determinations found via photometric fitting techniques, supporting the
accuracy and validity of photometric mass determinations in short period CVs.Comment: Accepted for publication in MNRAS (24th January 2012). 10 pages, 9
figures (black and white
The mass of the neutron star in Cyg X-2 (V1341 Cyg)
Cygnus X-2 is one of the brightest and longest known X-ray sources. We
present high resolution optical spectroscopy of Cyg X-2 obtained over 4 years
which gives an improved mass function of 0.69 +/- 0.03 Msun (1 sigma error). In
addition, we resolve the rotationally broadened absorption features of the
secondary star for the first time, deriving a rotation speed of vsin(i) = 34.2
+/- 2.5 km per s (1 sigma error) which leads to a mass ratio of q = M_c/M_x =
0.34 +/- 0.04 (1 sigma error), assuming a tidally-locked and Roche lobe-filling
secondary). Hence with the lack of X-ray eclipses (i.e. i <~ 73 degrees) we can
set firm 95% confidence lower limits to the neutron star mass of M_x > 1.27
Msun and to the companion star mass of M_c > 0.39 Msun. However, by
additionally requiring that the companion must exceed 0.75 Msun (as required
theoretically to produce a steady low-mass X-ray binary), then M_x > 1.88 Msun
and i < 61 degrees (95% confidence lower and upper limit, respectively),
thereby making Cyg X-2 the highest mass neutron star measured to date. If
confirmed this would set significant constraints on the equation of state of
nuclear matter.Comment: 16 pages, 4 figures, ApJ Letters, accepted, LaTeX, aasms4.st
V348 Puppis: a new SW Sex star in the period gap
We present time-resolved optical spectroscopy and photometry of the nova-like
cataclysmic variable V348 Puppis. The system displays the same spectroscopic
behaviour as SW Sex stars, so we classify V348 Pup as a new member of the
class. V348 Pup is the second SW Sex system (the first is V795 Herculis) which
lies in the period gap. The spectra exhibit enhanced HeII 4686 emission,
reminiscent of magnetic cataclysmic variables. The study of this emission line
gives a primary velocity semi-amplitude of K1 ~= 100 km/s. We have also derived
the system parameters, obtaining: M1 ~= 0.65 Msun, M2 ~= 0.20 Msun (q ~= 0.31),
i ~= 80 deg and K2 ~= 323 km/s. The spectroscopic behaviour of V348 Pup is very
similar to that of V795 Her, with the exception that V348 Pup shows deep
eclipses. We have computed the ``0.5-absorption'' spectrum of both systems,
obtaining spectra which resemble the absorption spectrum of a B0 V star. We
propose that absorption in SW Sex systems can be produced by a vertically
extended atmosphere which forms where the gas stream re-impacts the system,
either at the accretion disc or at the white dwarf's magnetosphere (assuming a
magnetic scenario).Comment: 6 pages, 10 figures, accepted for publication in MNRA
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