13 research outputs found
ROTSE observations of the young cluster IC 348
CCD observations of stars in the young cluster IC 348 were obtained from 2004
August to 2005 January with a 0.45 m ROTSEIIId robotic reflecting telescope at
the Turkish National Observatory site, Bakirlitepe, Turkey. The timing analysis
of selected stars whose X-Ray counterpart were detected by Chandra X-Ray
Observatory were studied. The time series of stars were searched for rotational
periodicity by using different period search methods. 35 stars were found to be
periodic with periods ranging from 0.74 to 32.3 days. Eighteen of the 35
periodic stars were new detections. Four of the new detections were CTTSs and
the others were WTTSs and G type (or unknown spectral class) stars. In this
study, we confirmed the stability of rotation periods of TTauri stars. The
periods obtained by Cohen et al. and us were different by 1%. We also confirmed
the 3.24 h pulsation period of H254 which is a delta Scuti type star as noted
by Ripepi et al. but the other periods detected by them were not found. We
examined correlation between X-ray luminosity and rotational period of our
sample of TTSs. There is a decline in the rotational period with X-ray
luminosity for late type TTSs.Comment: 15 pages, 14 figures, accepted for publication in Astronomical
Journa
Emission-Line Fluxes of Northern Planetary Nebulae
We present long slit spectrophotometric emission line fluxes of bright and
extended (<5 arcsec in diameter) Planetary Nebulae (PNe) selected from Acker et
al. 1992 catalog with suitable equitorial coordinates for Northern hemisphere.
In total, 17 PNe have been choosen and observed in 2008--2010. To measure
absolute fluxes, broad slit sizes, ranging from 3.5\arcsec to 7.5\arcsec were
used and thus equivalent widths of all observable emission line fluxes were
also calculated. Among 17 PNe's observed, line flux measurements of 12 of them
were made for the first time. This work also aims to extend the sky coverage of
emission line flux standards in Northern hemisphere (Dopita & Hua 1997 - 52 PNe
in Southern hemisphere; Wright et al. 2005 - 6 PNe in Northern hemisphere).
Electron temperatures and densities, and chemical abundances of these PNe were
also calculated in this work. These data is expected to lead the photometric or
spectrometric further work for absolute emission line flux measurements needed
for \hii regions, supernova remnants etc.Comment: 24 pages, 3 Figures, 21 Tables, Accepted for publication in
Publications of the Astronomical Society of Australi
Optical variabilities in Be/X-ray binary system:GRO J2058+42
We present an analysis of long-term optical monitoring observations and
optical spectroscopic observations of the counterpart to CXOU J205847.5+414637
(high mass X-ray binary system). We search for a variability in the light curve
of Be star. We used differential magnitudes in the time series analysis. The
variability search in the optical light curve was made by using different
algorithms. The reduction and analysis of spectra were done by using MIDAS and
its suitable packages. We have performed a frequency search which gave us the
value 2.404 1/day. This value is attributed to the non-radial pulsation of Be
star. H alpha emission line profiles always show double-peaked emissions with a
mean equivalent width of 2.31 \pm 0.19 \AA ~and a peak separation of 516 \pm 45
km/s. This suggests that Be star disk is still present. CXOU J205847.5+414637
is in X-ray quiescent state.Comment: 8 pages, 9 figures. To appear at Astronomy and Astrophysic
Recent RXTE/ASM and ROTSEIIId Observations of EXO 2030+375
Using the archival RXTE/ASM and SWIFT/BAT observations, the new orbital
phases of Type I outbursts of EXO 2030+375 are estimated. A possible
correlation between the Type II outburst and optical brightness variations is
investigated. In order to estimate the phases of Type I outbursts, we fitted
Gaussian profiles to the RXTE/ASM and SWIFT/BAT light curves. The time
corresponding to the maximum value of the profiles is treated as the arrival
time of Type I outburst. We used differential magnitudes in the time-series
analysis of the optical light curve. MIDAS and its suitable packages were used
to reduce and analyze the spectra. Prior to the Type II outburst, orbital
phases of Type I outbursts were delayed for 6 days after the periastron
passage, which is consistent with findings of Wilson et al., (2002, 2005).
After the giant Type II outburst, the phase of Type I outbursts underwent a
sudden shift of 13 days after the periastron passage. The amplitudes of Type I
outbursts were increased between MJD 52500 and 53500. These amplitudes then
decreased for 10 orbital cycles until the Type II outburst was triggered. If
the change of outburst amplitudes correlated with the mass accretion, then
during the decrease of these amplitudes mass should be deposited in a disk
around neutron star temporarily. The release of this stored mass may ignite the
Type II outburst. We report that the optical light curve became fainter by 0.4
mag during the decrease of amplitude of the Type I outbursts. The observed
H profiles and their equivalent widths during the decay and after the
giant outburst are consistent with previous observations of the system.Comment: to appear at Astronomy and Astrophysic
Optical and X-ray Outbursts of Be/X-ray binary system SAX J2103.5+4545
We present the relations between Halpha equivalent width, optical brightness
and X-ray flux of Be/X-ray binary system SAX J2103.5+4545, by analyzing the
optical photometric and spectroscopic observations together with the X-ray
observations.
In the photometric observations PSF photometry were applied using MIDAS and
its DAOPHOT package. The reduction and analysis of spectra were done by using
MIDAS and its suitable packages. The X-ray outburst of the system occurred just
after the optical outburst. The nearly symmetric Halpha emission line profiles
observed during the beginning of optical outburst turn into asymmetric profiles
with increased EW values during the dissipation of Be disc. Halpha lines
changed from emission to absorption during the observation period. The observed
double peaked HeI emission lines might come from the accretion disc of neutron
star which is temporarily formed at the time of X-ray outburst.Comment: to be pubished at Astronomy and Astrophysics on June 200
Status of the ROTSE-III telescope network
ROTSE-III is a homogeneous worldwide array of 4 robotic telescopes. They were designed to provide optical observations of γ-ray burst (GRB) afterglows as close as possible to the start of γ-ray emission. ROTSE-III is fulfilling its potential for GRB science, and provides optical observations for a variety of astrophysical sources in the interim between GRB events
Prompt Optical Detection of GRB 050401 with ROTSE-IIIa
The ROTSE-IIIa telescope at Siding Spring Observatory, Australia, detected
prompt optical emission from Swift GRB 050401. In this letter, we present
observations of the early optical afterglow, first detected by the ROTSE-IIIa
telescope 33 s after the start of gamma-ray emission, contemporaneous with the
brightest peak of this emission. This GRB was neither exceptionally long nor
bright. This is the first prompt optical detection of a GRB of typical duration
and luminosity. We find that the early afterglow decay does not deviate
significantly from the power-law decay observable at later times, and is
uncorrelated with the prompt gamma-ray emission. We compare this detection with
the other two GRBs with prompt observations, GRB 990123 and GRB 041219a. All
three bursts exhibit quite different behavior at early times.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letter
The Anomalous Early Afterglow of GRB 050801
The ROTSE-IIIc telescope at the H.E.S.S. site, Namibia, obtained the earliest
detection of optical emission from a Gamma-Ray Burst (GRB), beginning only 21.8
s from the onset of Swift GRB 050801. The optical lightcurve does not fade or
brighten significantly over the first ~250 s, after which there is an
achromatic break and the lightcurve declines in typical power-law fashion. The
Swift/XRT also obtained early observations starting at 69 s after the burst
onset. The X-ray lightcurve shows the same features as the optical lightcurve.
These correlated variations in the early optical and X-ray emission imply a
common origin in space and time. This behavior is difficult to reconcile with
the standard models of early afterglow emission.Comment: 5 pages, 1 figure. Accepted for publication in ApJ Letter
Optical Lightcurve & Cooling Break of GRB 050502A
We present lightcurves of the afterglow of GRB050502A, including very early
data at t-t_{GRB} < 60s. The lightcurve is composed of unfiltered ROTSE-IIIb
optical observations from 44s to 6h post-burst, R-band MDM observations from
1.6 to 8.4h post-burst, and PAIRITEL J H K_s observations from 0.6 to 2.6h
post-burst. The optical lightcurve is fit by a broken power law, where
t^{alpha} steepens from alpha = -1.13 +- 0.02 to alpha = -1.44 +- 0.02 at
\~5700s. This steepening is consistent with the evolution expected for the
passage of the cooling frequency nu_c through the optical band. Even in our
earliest observation at 44s post-burst, there is no evidence that the optical
flux is brighter than a backward extrapolation of the later power law would
suggest. The observed decay indices and spectral index are consistent with
either an ISM or a Wind fireball model, but slightly favor the ISM
interpretation. The expected spectral index in the ISM interpretation is
consistent within 1 sigma with the observed spectral index beta = -0.8 +- 0.1;
the Wind interpretation would imply a slightly (~2 sigma) shallower spectral
index than observed. A small amount of dust extinction at the source redshift
could steepen an intrinsic spectrum sufficiently to account for the observed
value of beta. In this picture, the early optical decay, with the peak at or
below 4.7e14 Hz at 44s, requires very small electron and magnetic energy
partitions from the fireball.Comment: 22 pages, including 3 tables and 1 figure, Accepted by Ap
Exploring Broadband GRB Behavior During gamma-ray Emission
The robotic ROTSE-III telescope network detected prompt optical emission
contemporaneous with the gamma-ray emission of Swift events GRB051109A and
GRB051111. Both datasets have continuous coverage at high signal-to-noise
levels from the prompt phase onwards, thus the early observations are readily
compared to the Swift XRT and BAT high energy detections. In both cases, the
optical afterglow is established, declining steadily during the prompt
emission. For GRB051111, there is evidence of an excess optical component
during the prompt emission. The component is consistent with the flux
spectrally extrapolated from the gamma-rays, using the gamma-ray spectral
index. A compilation of spectral information from previous prompt detections
shows that such a component is unusual. The existence of two prompt optical
components - one connected to the high-energy emission, the other to separate
afterglow flux, as indicated in GRB051111 - is not compatible with a simple
``external-external'' shock model for the GRB and its afterglow.Comment: ApJ accepted. 32 pages (in preprint form), 5 tables, 5 figure