149 research outputs found
A Search For Supernova Remnants in The Nearby Spiral Galaxy M74 (NGC 628)
We have identified nine new SNR candidates in M74 with [S II]/H
0.4 as the basic criterion. We obtain [S II]/H ratio in the
range from 0.40 to 0.91 and H intensities from 2.8
erg cm s to 1.7 erg cm s. We
also present spectral follow-up observations of the SNR candidates and can
confirm only three of them (SNR2, SNR3, and SNR5). The lack of confirmation for
the rest might be due to the contamination by the nearby H II emission regions
as well as due to the inaccurate positioning of the long slit on these objects.
In addition, we search the Observatory archival data for the X-ray
counterparts to the optically identified candidates. We find positional
coincidence with only three SNR candidates, SNR1, SNR2, and SNR8. The spectrum
of SNR2 yields a shock temperature of 10.8 keV with an ionization timescale of
1.6 10 s cm indicating a relatively young remnant in an
early Sedov phase which is not supported by our optical wavelength analysis.
Given the high luminosity of 10 erg s and the characteristics of
the X-ray spectrum, we favor an Ultra Luminous X-ray Source interpretation for
this source associated with an SNR. We calculate an X-ray flux upper limit of
9.0 erg cm s for the rest of the SNRs
including spectroscopically identified SNR3 and SNR5.Comment: 10 pages, 8 figures, accepted to be published in A&
The Detection of a 3.5-h Period in the Classical Nova Velorum 1999 (V382 Vel) and the Long Term Behavior of the Nova Light Curve
We present CCD photometry, light curve and time series analysis of the
classical nova V382 Vel (N Vel 1999). The source was observed for 2 nights in
2000, 21 nights in 2001 and 7 nights in 2002 using clear filters. We report the
detection of a distinct period in the light curve of the nova P=0.146126(18) d
(3.5 h). The period is evident in all data sets, and we interpret it as the
binary period of the system. We also measured an increase in the amplitude
modulation of the optical light (in magnitude) by more than 55% from 2000 to
2001 and about 64% from 2001 to 2002. The pulse profiles in 2001 show
deviations from a pure sinusoidal shape which progressively become more
sinusoidal by 2002. The main cause of the variations in 2001 and 2002 can be
explained with the occultation of the accretion disk by the secondary star. We
interpret the observed deviations from a pure sinusoidal shape as additional
flux resulting from the aspect variations of the irradiated face of the
secondary star.Comment: 16 pages and 4 figures, accepted as it stands to be published in the
Astronomical Journal (AJ
Evidence for ablated flows in the shell of nova DQ Her
High-resolution longslit Halpha spectra of the shell of the old nova DQ Her
have been obtained with the William Herschel Telescope using the ISIS
spectrograph. An equatorial expansion velocity of 370+/-14 km/s is derived from
the spectra which, in conjunction with a narrowband Halpha image of the
remnant, allows a distance estimate of 525+/-28 pc. An equatorial ring which
exhibits enhanced [NII] emission has also been detected and the inclination
angle of the shell is found to be 86.8+/-0.2 degrees with respect to the line
of sight. The spectra also reveal tails extending from the clumps in the shell,
which have a radial velocity increasing along their length. This suggests the
presence of a stellar wind, collimated in the polar direction, which ablates
fragments of material from the clumps and accelerates them into its stream up
to a terminal velocity of order 800-900 km/s.Comment: 7 pages, 6 figure
The inclination angle and mass of the black hole in XTE J1118+480
We have obtained optical and infrared photometry of the quiescent soft X-ray transient XTE J1118+480. In addition to optical and J-band variations, we present H- and Ks-band ellipsoidal variations for this system. We model the variations in all bands simultaneously with the WD98 light curve modeling code. The infrared colors of the secondary star in this system are consistent with those of a K7 V, while there is evidence for light from the accretion disk in the optical. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is 68 degrees ±2 degrees. This inclination angle corresponds to a primary black hole mass of 8.53+/-0.60 M☉. Based on the derived physical parameters and infrared colors of the system, we determine a distance of 1.72+/-0.10 kpc to XTE J1118+480
New X-ray observations of the old nova CP Puppis and of the more recent nova V351 Pup
We present X-ray observations of the field containing Nova Puppis 1942 (CP
Pup) and Nova Puppis 1991 (V351 Pup), done with ASCA in 1998, and with
XMM-Newton in 2005. The X-ray and UV luminosity of CP Pup seem to have remained
approximately constant since the last X-ray observations of the 1980'ies, while
the optical luminosity has decreased. The X-ray properties of this nova are
explained by a high mass white dwarf accreting at low rate, in agreement with
the nova theory given the large amplitude and other characteristics of the 1942
outburst.
Assuming a distance of 1600 pc, the X-ray luminosity of CP Pup is L=2.2 x
10(33) erg/s in the 0.15-10 keV range covered with EPIC, compatible with a
magnetic system. The RGS grating spectrum shows a few prominent emission lines,
and it is fitted with a cooling flow with mass accretion rate mdot <= 1.6 x
10(-10) msol/year. We detected also the O VII complex at 21.6-21.8 A that does
not arise in the cooling flow. Most likely this feature originates in a wind or
in the nova shell. The RGS and EPIC spectra are fitted only with thermal models
with a very high shock temperature, T>60 keV, indicating a white dwarf with
M>1.1 M(sun). The X-ray flux is modulated with the spectroscopic period of 1.47
hours detected in the optical. Since CP Pup is not an eclipsing system, this is
better understood if magnetic accretion occurs: we discuss this possibility and
its implications in detail. V351 Pup (N Pup 1991) was detected with XMM-Newton,
but not with ASCA. It is a faint, non-super-soft X-ray source with luminosity
L(x) =~ 3 x 10(31) erg/s, a factor of 50 less than measured with ROSAT in 1993.Comment: in press on the Astrophysical Journa
Astrophysical Fluids of Novae: High Resolution Pre-decay X-ray spectrum of V4743 Sagittarii
Eight X-ray observations of V4743 Sgr (2002), observed with Chandra and
XMM-Newton are presented. The nova turned off some time between days 301.9 and
371, and the X-ray flux subsequently decreased from day 301.9 to 526 following
an exponential decline time scale of days. We use the absorption
lines present in the SSS spectrum for diagnostic purposes, and characterize the
physics and the dynamics of the expanding atmosphere during the explosion of
the nova. The information extracted from this first stage is then used as input
for computing full photoionization models of the ejecta in V4743 Sgr. The SSS
spectrum is modeled with a simple black-body and multiplicative Gaussian lines,
which provides us of a general kinematical picture of the system, before it
decays to its faint phase (Ness et al. 2003). In the grating spectra taken
between days 180.4 and 370, we can resolve the line profiles of absorption
lines arising from H-like and He-like C, N, and O, including transitions
involving higher principal quantum numbers. Except for a few interstellar
lines, all lines are significantly blue-shifted, yielding velocities between
1000 and 6000 km/s which implies an ongoing mass loss. It is shown that
significant expansion and mass loss occur during this phase of the explosion,
at a rate . Our measurements show that the efficiency of the amount of
energy used for the motion of the ejecta, defined as the ratio between the
kinetic luminosity and the radiated luminosity , is
of the order of one.Comment: 25 pages, 9 figures. Accepted in book: Recent Advances in Fluid
Dynamics with Environmental Applications, pp.365-39
The Inclination Angle of and Mass of the Black Hole in XTE J1118+480
We have obtained optical and infrared photometry of the quiescent soft X-ray
transient XTE J1118+480. In addition to optical and J-band variations, we
present the first observed H- and K_s-band ellipsoidal variations for this
system. We model the variations in all bands simultaneously with the WD98 light
curve modeling code. The infrared colors of the secondary star in this system
are consistent with a K7V, while there is evidence for light from the accretion
disk in the optical. Combining the models with the observed spectral energy
distribution of the system, the most likely value for the orbital inclination
angle is 68 +/- 2 deg. This inclination angle corresponds to a primary black
hole mass of 8.53 +/- 0.60 M_sun. Based on the derived physical parameters and
infrared colors of the system, we determine a distance of 1.72 +/- 0.10 kpc to
XTE J1118+480.Comment: 6 pages, 3 figures, To appear in ApJ 01 May 2006 issu
X-ray variations in the inner accretion flow of Dwarf Novae
We show for five DN systems, SS Cyg, VW Hyi, RU Peg, WW Cet and T Leo that
the UV and X-ray power spectra of their time variable light curves are similar
in quiescence. All of them show a break in their power spectra, which in the
framework of the model of propagating fluctuations indicates inner disk
truncation. We derive the inner disk radii for these systems in a range
(10-3) cm. We analyze the RXTE data of SS Cyg in outburst and
compare it with the power spectra, obtained during the period of quiescence. We
show that during the outburst the disk moves towards the white dwarf and
recedes as the outburst declines. We calculate the correlation between the
simultaneous UV and X-ray light curves of the five DN studied in this work,
using the XMM-Newton data obtained in the quiescence and find X-ray time lags
of 96-181 sec. This can be explained by the travel time of matter from a
truncated inner disk to the white dwarf surface. We suggest that, in general,
DN may have truncated accretion disks in quiescence which can also explain the
UV and X-ray delays in the outburst stage and that the accretion may occur
through coronal flows in the disk (e.g., rotating accretion disk coronae).
Within a framework of the model of propagating fluctuations the comparison of
the X-ray/UV time lags observed by us in the case of DN systems with those,
detected for a magnetic Intermediate Polar allows us to make a rough estimate
of the viscosity parameter in the innermost parts of the
accretion flow of DN systems.Comment: 10 pages, 11 figures; accepted for publication in A&A as it stand
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