34 research outputs found
Jet-Induced Nucleosynthesis in Misaligned Microquasars
The jet axes and the orbital planes of microquasar systems are usually
assumed to be approximately perpendicular, eventhough this is not currently an
observational requirement. On the contrary, in one of the few systems where the
relative orientations are well-constrained, V4641Sgr, the jet axis is known to
lie not more than ~36 degrees from the binary plane. Such a jet, lying close to
the binary plane, and traveling at a significant fraction of the speed of light
may periodically impact the secondary star initiating nuclear reactions on its
surface. The integrated yield of such nuclear reactions over the age of the
binary system (less the radiative mass loss) will detectably alter the
elemental abundances of the companion star. This scenario may explain the
anomalously high Li enhancements (roughly ~20-200 times the sun's photospheric
value; or, equivalently, 0.1-1 times the average solar system value) seen in
the companions of some black-hole X-ray binary systems. (Such enhancements are
puzzling since Li nuclei are exceedingly fragile - being easily destroyed in
the interiors of stars - and Li would be expected to be depleted rather than
enhanced there.) Gamma-ray line signatures of the proposed process could
include the 2.22 MeV neutron capture line as well as the 0.478 MeV 7Li*
de-excitation line, both of which may be discernable with the INTEGRAL
satellite if produced in an optically thin region during a large outburst. For
very energetic jets, a relatively narrow neutral pion gamma-decay signature at
67.5 MeV could also be measurable with the GLAST satellite. We argue that about
10-20% of all microquasar systems ought to be sufficiently misaligned as to be
undergoing the proposed jet-secondary impacts.Comment: ApJ, accepted. Includes referee's suggestions and some minor
clarifications over previous versio
The 3-Dimensional Structure of HH 32 from GMOS IFU Spetroscopy
We present new high resolution spectroscopic observations of the Herbig-Haro
object HH 32 from System Verification observations made with the GMOS IFU at
Gemini North Observatory. The 3D spectral data covers a 8''.7 x 5''.85 spatial
field and 4820 - 7040 Angstrom spectral region centered on the HH~32 A knot
complex. We show the position-dependent line profiles and radial velocity
channel maps of the Halpha line, as well as line ratio velocity channel maps of
[OIII]5007/Halpha, [OI]6300/Halpha, [NII]6583/Halpha, [SII](6716+6730)/Halpha
and [SII]6716/6730. We find that the line emission and the line ratios vary
significantly on spatial scales of ~1'' and over velocities of ~50 km/s. A
``3/2-D'' bow shock model is qualitatively successful at reproducing the
general features of the radial velocity channel maps, but it does not show the
same complexity as the data and it fails to reproduce the line ratios in our
high spatial resolution maps. The observations of HH 32 A show two or three
superimposed bow shocks with separations of ~3'', which we interpret as
evidence of a line of sight superposition of two or three working surfaces
located along the redshifted body of the HH 32 outflow.Comment: Accepted for Publication in the Astronomical Journal (January 2004
Detection of hard X-rays from a Class I protostar in the HH24-26 region in the Orion Molecular Cloud
We observed the HH24-26 region in the L1630 Orion molecular cloud complex
with the X-ray observatory ASCA in the 0.510 keV band. X-ray emission was
detected from the T Tauri star SSV61 and from the region where the Class I
protostars
SSV63E and SSV63W are located (hereafter SSV63E+W). The spectra of both
SSV63E+W and SSV61 are well explained by an optically thin thermal plasma
model. The spectrum of the T Tauri star SSV61 has a low temperature of
(0.71.2) keV and a moderate absorption of (0.91.7)
cm, while that of the protostar SSV63E+W has a high
temperature of (3.37.9) keV and a heavy absorption of
(1.21.8) cm. The X-ray light curve
of SSV63E+W showed a flare during the observation. The peak flux reached about
9 times that of the quiescent flux. The temperature and the absorption column
density do not change conspicuously during the flare. The 0.510 keV
luminosity of SSV63E+W was about erg s in the quiescent
state. The present detection of hard X-rays from SSV63E+W is remarkable,
because this is the first X-ray detection of a protostar in Orion.Comment: 14 pages, 3 postscript figures, uses aasms4.st
Radio Emission from the Composite Supernova Remnant G326.3-1.8 (MSH15-56)
High resolution radio observations of the composite supernova remnant (SNR)
G326.3-1.8 or MSH 15-56 with the Australia Telescope Compact Array show details
of both the shell and the bright plerion which is offset about 1/3 of the
distance from the center of the SNR to the shell. The shell appears to be
composed of thin filaments, typical of older shell SNRs. The central part of
the elongated plerion is composed of a bundle of parallel ridges which bulge
out at the ends and form a distinct ring structure on the northwestern end. The
magnetic field with a strength of order 45 microGauss, is directed along the
axis of the ridges but circles around the northwestern ring. This plerion is
large and bright in the radio but is not detected in x-ray or optical
wavelengths. There is, however, a faint hard x-ray feature closer to the shell
outside the plerion. Perhaps if the supernova explosion left a rapidly moving
magnetar with large energy input but initially rapid decay of both relativistic
particles and magnetic field, the observed differences with wavelength could be
explained.Comment: 15 pages, 10 figures, accepted by Ap
New Herbig-Haro Objects and Giant Outflows in Orion
We present the results of a photographic and CCD imaging survey for
Herbig-Haro (HH) objects in the L1630 and L1641 giant molecular clouds in
Orion. The new HH flows were initially identified from a deep H-alpha film from
the recently commissioned AAO/UKST H-alpha Survey of the southern sky. Our
scanned H-alpha and broad band R images highlight both the improved resolution
of the H-alpha survey and the excellent contrast of the H-alpha flux with
respect to the broad band R. Comparative IVN survey images allow us to
distinguish between emission and reflection nebulosity. Our CCD H-alpha, [SII],
continuum and I band images confirm the presence of a parsec-scale HH flow
associated with the Ori I-2 cometary globule and several parsec-scale strings
of HH emission centred on the L1641-N infrared cluster. Several smaller
outflows display one-sided jets. Our results indicate that for declinations
south of -6 degrees in L1641, parsec-scale flows appear to be the major force
in the large-scale movement of optical dust and molecular gas.Comment: 14 pages, Latex using MN style, 21 figures in JPEG format. Higher
resolution figures available from S.L. Mader. Accepted by MNRAS. Email
contact for higher resolution images: [email protected]
On the Identification of High Mass Star Forming Regions using IRAS: Contamination by Low-Mass Protostars
We present the results of a survey of a small sample (14) of low-mass
protostars (L_IR < 10^3 Lsun) for 6.7 GHz methanol maser emission performed
using the ATNF Parkes radio telescope. No new masers were discovered. We find
that the lower luminosity limit for maser emission is near 10^3 Lsun, by
comparison of the sources in our sample with previously detected methanol maser
sources. We examine the IRAS properties of our sample and compare them with
sources previously observed for methanol maser emission, almost all of which
satisfy the Wood & Churchwell criterion for selecting candidate UCHII regions.
We find that about half of our sample satisfy this criterion, and in addition
almost all of this subgroup have integrated fluxes between 25 and 60 microns
that are similar to sources with detectable methanol maser emission. By
identifying a number of low-mass protostars in this work and from the
literature that satisfy the Wood & Churchwell criterion for candidate UCHII
regions, we show conclusively for the first time that the fainter flux end of
their sample is contaminated by lower-mass non-ionizing sources, confirming the
suggestion by van der Walt and Ramesh & Sridharan.Comment: 8 pages with 2 figures. Accepted by Ap
Three-dimensional hydrodynamical simulations of the large scale structure of W50-SS433
We present 3D hydrodynamical simulations of a precessing jet propagating inside a supernova remnant (SNR) shell, particularly applied to the W50-SS433 system in a search for the origin of its peculiar elongated morphology. Several runs were carried out with different values for the mass loss rate of the jet, the initial radius of the SNR, and the opening angle of the precession cone. We found that our models successfully reproduce the scale and morphology of W50 when the opening angle of the jets is set to 10 or if this angle linearly varies with time. For these models, more realistic runs were made considering that the remnant is expanding into an interstellar medium (ISM) with an exponential density profile (as HI observations suggest). Taking into account all these ingredients, the large scale morphology of the W50-SS 433 system, including the asymmetry between the lobes (formed by the jet-SNR interaction), is well reproduced.Fil: Zavala, Jesús. Universidad Nacional Autónoma de México; MéxicoFil: Velázquez, Pablo F.. Universidad Nacional Autónoma de México; MéxicoFil: Cerqueira, Adriano H. Universidade Estadual de Santa Cruz; BrasilFil: Dubner, Gloria Mabel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
Warping and precession in galactic and extragalactic accretion disks
The Bardeen-Petterson general relativistic effect has been suggested as the
mechanism responsible for precession in some accretion disk systems. Here we
examine separately four mechanisms (tidally-induced, irradiation-induced,
magnetically-induced and Bardeen-Petterson-induced) that can lead to warping
and precession. We use a sample of eight X-ray binaries and four Active
Galactic Nuclei (AGNs) that present signatures of warping and/or precession in
their accretion disks to explore the viability of the different mechanisms. For
the X-ray binaries SMC X-1 and 4U 1907+09 all four mechanisms provide
precession periods compatible with those observed, while for Cyg X-1 and the
active galaxies Arp 102B and NGC 1068, only two mechanisms are in agreement
with the observations. The irradiation-driven instability seems incapable of
producing the inferred precession of the active galaxies in our sample, and the
tidally-induced precession can probably be ruled out in the case of Arp 102B.
Perhaps the best case for a Bardeen-Petterson precession can be achieved for
NGC 1068. Our results show that given the many observational uncertainties that
still exist, it is extremely difficult to confirm unambiguously that the
Bardeen-Petterson effect has been observed in any of the other sources of our
sample.Comment: 35 pages, 8 figures, accepted for publication in The Astrophysical
Journa
X-ray Study of the Intermediate-Mass Young Stars Herbig Ae/Be Stars
We present the ASCA results of intermediate-mass pre-main-sequence stars
(PMSs), or Herbig Ae/Be stars (HAeBes). Among the 35 ASCA pointed-sources, we
detect 11 plausible X-ray counterparts. X-ray luminosities of the detected
sources in the 0.5-10 keV band are in the range of log LX ~30-32 ergs s-1,
which is systematically higher than those of low-mass PMSs. This fact suggests
that the contribution of a possible low-mass companion is not large. Most of
the bright sources show significant time variation, particularly, two HAeBes -
MWC 297 and TY CrA - exhibit flare-like events with long decay timescales
(e-folding time ~ 10-60 ksec). These flare shapes are similar to those of
low-mass PMSs. The X-ray spectra are successfully reproduced by an absorbed one
or two-temperature thin-thermal plasma model. The temperatures are in the range
of kT ~1-5 keV, which are significantly higher than those of main-sequence OB
stars (kT < 1 keV). These X-ray properties are not explained by wind driven
shocks, but are more likely due to magnetic activity. On the other hand, the
plasma temperature rises as absorption column density increases, or as HAeBes
ascend to earlier phases. The X-ray luminosity reduces after stellar age of a
few x10^6 years. X-ray activity may be related to stellar evolution. The age of
the activity decay is apparently near the termination of jet or outflow
activity. We thus hypothesize that magnetic activity originates from the
interaction of the large scale magnetic fields coupled to the circumstellar
disk. We also discuss differences in X-ray properties between HAeBes and
main-sequence OB stars.Comment: 51 pages, 17 figures, accepted by Ap