143 research outputs found
Outer jet X-ray and radio emission in R Aquarii: 1999.8 to 2004.0
Chandra and VLA observations of the symbiotic star R Aqr in 2004 reveal
significant changes over the three to four year interval between these
observations and previous observations taken with the VLA in 1999 and with
Chandra in 2000. This paper reports on the evolution of the outer thermal X-ray
lobe-jets and radio jets. The emission from the outer X-ray lobe-jets lies
farther away from the central binary than the outer radio jets, and comes from
material interpreted as being shock heated to ~10^6 K, a likely result of
collision between high speed material ejected from the central binary and
regions of enhanced gas density. Between 2000 and 2004, the Northeast (NE)
outer X-ray lobe-jet moved out away from the central binary, with an apparent
projected motion of ~580 km s^-1. The Southwest (SW) outer X-ray lobe-jet
almost disappeared between 2000 and 2004, presumably due to adiabatic expansion
and cooling. The NE radio bright spot also moved away from the central binary
between 2000 and 2004, but with a smaller apparent velocity than of the NE
X-ray bright spot. The SW outer lobe-jet was not detected in the radio in
either 1999 or 2004. The density and mass of the X-ray emitting material is
estimated. Cooling times, shock speeds, pressure and confinement are discussed.Comment: 23 pages, 8 figure
Collapse of Randomly Linked Polymers
We consider polymers in which M randomly selected pairs of monomers are
restricted to be in contact. Analytical arguments and numerical simulations
show that an ideal (Gaussian) chain of N monomers remains expanded as long as
M<<N. This result is inconsistent with results obtained from free energy
considerations by Brygelson and Thirumalai (PRL76, 542 (1996)).Comment: 1 page, 1 postscript figure, LaTe
The ultraviolet spectrum of HH 24A and its relation to optical spectra
The spectrum of the brightest part (HH 24A) of the complex Herbig-Haro object HH 24 in the short wavelength UV range was studied. The object is of special interest since it is known that in the optical range the continuum is due to dust scattered light originating in a young stellar object while the shock excited emission lines are formed in HH 24A itself. The spectrum shows only a continuum or a quasi-continuum and is not comparable to that of the typical high excitation object like HH1 or HH2 nor to that of a low excitation object like HH3 or HH47
The constant-velocity highly collimated outflows of the planetary nebula He 2-90
We present high-dispersion echelle spectroscopic observations and a
narrow-band [N II] image of the remarkable jet-like features of He 2-90. They
are detected in the echelle spectra in the H-alpha and [N II] lines but not in
other nebular lines. The [N II]/H-alpha ratio is uniformly high, ~1. The
observed kinematics reveals bipolar collimated outflows in the jet-like
features and shows that the southeast (northwest) component expands towards
(away from) the observer at a remarkably constant line-of-sight velocity,
26.0+-0.5 km/s. The observed expansion velocity and the opening angle of the
jet-like features are used to estimate an inclination angle of ~5 degrees with
respect to the sky plane and a space expansion velocity of ~290 km/s. The
spectrum of the bright central nebula reveals a profusion of Fe lines and
extended wings of the H-alpha line, similar to those seen in symbiotic stars
and some young planetary nebulae that are presumed to host a mass-exchanging
binary system. If this is the case for He 2-90, the constant velocity and
direction of the jets require a very stable dynamic system against precession
and warping.Comment: 8 pages (emulate ApJ), 5 figure, 1 tabl
Mz 3, a Multipolar Nebula in the Making
The nebula Mz 3 has arguably the most complex bipolar morphology, consisting
of three nested pairs of bipolar lobes and an equatorial ellipse. Its three
pairs of bipolar lobes share the same axis of symmetry, but have very different
opening angles and morphologies: the innermost pair of bipolar lobes shows
closed lobe morphology, while the other two have open lobes with cylindrical
and conical shapes, respectively. We have carried out high-dispersion
spectroscopic observations of Mz 3, and detected distinct kinematic properties
among the different morphological components. The expansion characteristics of
the two outer pairs of lobes suggest that they originated in an explosive
event, whereas the innermost pair of lobes resulted from the interaction of a
fast wind with the surrounding material. The equatorial ellipse is associated
with a fast equatorial outflow which is unique among bipolar nebulae. The
dynamical ages of the different structures in Mz 3 suggest episodic bipolar
ejections, and the distinct morphologies and kinematics among these different
structures reveal fundamental changes in the system between these episodic
ejections.Comment: To be published in the October issue of The Astronomical Journal. 16
pages, 10 figures. For full resolution figures, send requests to the Author
[email protected]
Precession of collimated outflows from young stellar objects
We consider several protostellar systems where either a precessing jet or at
least two misaligned jets have been observed. We assume that the precession of
jets is caused by tidal interactions in noncoplanar binary systems. For Cep E,
V1331 Cyg and RNO 15-FIR the inferred orbital separations and disk radii are in
the range 4-160 AU and 1-80 AU, respectively, consistent with those expected
for pre-main sequence stars. Furthermore, we assume or use the fact that the
source of misaligned outflows is a binary, and evaluate the lengthscale over
which the jets should precess as a result of tidal interactions. For T Tau, HH1
VLA 1/2 and HH 24 SVS63, it may be possible to detect a bending of the jets
rather than 'wiggling'. In HH 111 IRS and L1551 IRS5, 'wiggling' may be
detected on the current observed scale. Our results are consistent with the
existence of noncoplanar binary systems in which tidal interactions induce jets
to precess.Comment: 5 pages (including 1 figure), LaTeX, uses emulateapj.sty, to be
published in ApJ Letters, also available at
http://www.ucolick.org/~ct/home.html and
http://www.tls-tautenburg.de/research/research.htm
The Planetary Mass Companion 2MASS1207-3932 B: Temperature, Mass and Evidence for an Edge-On Disk
We present J-band imaging and H+K-band low-resolution spectroscopy of
2MASS1207-3932 AB, obtained with VLT NACO. For the putative planetary mass
secondary, we find J = 20.0+/-0.2 mag. The HK spectra of both components imply
low gravity, and a dusty atmosphere for the secondary. Comparisons to synthetic
spectra yield Teff_A ~ 2550+/-150K, and Teff_B ~ 1600+/-100K, consistent with
their late-M and mid-to-late L types. For these Teff, and an age of 5-10 Myrs,
evolutionary models imply M_A ~ 24+/-6 M_Jup and M_B ~ 8+/-2 M_Jup. Independent
comparisons of these models to the observed colors, spanning ~I to L', also
yield the same masses and temperatures. Our primary mass agrees with other
recent analyses; however, our secondary mass, while still in the planetary
regime, is 2-3 times larger than claimed previously. This discrepancy can be
traced to the luminosities: while the absolute photometry and Mbol of the
primary agree with theoretical predictions, the secondary is ~ 2.5+/-0.5 mag
fainter than expected in all bands from I to L' and in Mbol. This accounts for
the much lower secondary mass (and temperature) derived earlier. We argue that
this effect is highly unlikely to result from a variety of model-related
problems, and is instead real. This conclusion is bolstered by the absence of
any luminosity problems in either the primary, or in AB Pic B which we also
analyse. We therefore suggest grey extinction in 2M1207B, due to occlusion by
an edge-on circum-secondary disk. This is consistent with the observed
properties of edge-on disks around T Tauri stars, and with the known presence
of a high-inclination evolved disk around the primary. Finally, the system's
implied mass ratio of ~0.3 suggests a binary-like formation scenario.
(abridged)Comment: Accepted by The Astrophysical Journal, 43 pages text + 16 figs + 1
tabl
Hydrodynamical simulations of the jet in the symbiotic star MWC 560 III. Application to X-ray jets in symbiotic stars
In papers I and II in this series, we presented hydrodynamical simulations of
jet models with parameters representative of the symbiotic system MWC 560.
These were simulations of a pulsed, initially underdense jet in a high density
ambient medium. Since the pulsed emission of the jet creates internal shocks
and since the jet velocity is very high, the jet bow shock and the internal
shocks are heated to high temperatures and should therefore emit X-ray
radiation. In this paper, we investigate in detail the X-ray properties of the
jets in our models. We have focused our study on the total X-ray luminosity and
its temporal variability, the resulting spectra and the spatial distribution of
the emission. Temperature and density maps from our hydrodynamical simulations
with radiative cooling presented in the second paper are used together with
emissivities calculated with the atomic database ATOMDB. The jets in our models
show extended and variable X-ray emission which can be characterized as a sum
of hot and warm components with temperatures that are consistent with
observations of CH Cyg and R Aqr. The X-ray spectra of our model jets show
emission line features which correspond to observed features in the spectra of
CH Cyg. The innermost parts of our pulsed jets show iron line emission in the
6.4 - 6.7 keV range which may explain such emission from the central source in
R Aqr. We conclude that MWC 560 should be detectable with Chandra or
XMM-Newton, and such X-ray observations will provide crucial for understanding
jets in symbiotic stars.Comment: 10 pages, 12 figures, accepted for publication in ApJ, uses
emulateap
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