112 research outputs found
Near-infrared Observations of Be/X-ray Binary Pulsar A0535+262
We present results obtained from an extensive near-infrared spectroscopic and
photometric observations of the Be/X-ray binary A0535+262/HDE 245770 at
different phases of its ~111 day orbital period. This observation campaign is a
part of the monitoring programme of selective Be/X-ray binary systems aimed at
understanding the X-ray and near-IR properties at different orbital phases,
especially during the periastron passage of the neutron star. The near-IR
observations were carried out using the 1.2 m telescope at Mt. Abu IR
observatory. Though the source was relatively faint for spectroscopic
observations with 1.2 m telescope, we monitored the source during the 2011
February--March giant outburst to primarily investigate whether any drastic
changes in the near-IR JHK spectra take place at the periastron passage.
Changes of such a striking nature were expected to be detectable in our
spectra. Photometric observations of the Be star show a gradual and systematic
fading in the JHK light curves since the onset of the X-ray outburst that could
suggest a mild evacuation/truncation of the circumstellar disc of the Be
companion. Near-IR spectroscopy of the object shows that the JHK spectra are
dominated by the emission lines of hydrogen Brackett and Paschen series and HeI
lines at 1.0830, 1.7002 and 2.0585 micron. The presence of all hydrogen
emission lines in the JHK spectra, along with the absence of any significant
change in the continuum of the Be companion during X-ray quiescent and X-ray
outburst phases suggest that the near-IR line emitting regions of the disc are
not significantly affected during the X-ray outburst.Comment: 10 Pages, 5 Figures, Accepted for publication in Res. in Astronomy
and Astrophysic
Near-infrared Observations of Nova V574 Puppis (2004)
We present results obtained from extensive near-infrared spectroscopic and
photometric observations of nova V574 Pup during its 2004 outburst. The
observations were obtained over four months, starting from 2004 November 25
(four days after the nova outburst) to 2005 March 20. The near-IR JHK light
curve is presented - no evidence is seen from it for dust formation to have
occurred during our observations. In the early decline phase, the JHK spectra
of the nova are dominated by emission lines of hydrogen Brackett and Paschen
series, OI, CI and HeI. We also detect the fairly uncommon Fe II line at 1.6872
micron in the early part of our observations. The strengths of the HeI lines at
1.0830 micron and 2.0585 micron are found to become very strong towards the end
of the observations indicating a progression towards higher excitation
conditions in the nova ejecta. The width of the emission lines do not show any
significant change during the course of our observations. The slope of the
continuum spectrum was found to have a lambda^{-2.75} dependence in the early
stages which gradually becomes flatter with time and changes to a free-free
spectral dependence towards the later stages. Recombination analysis of the HI
lines shows deviations from Case B conditions during the initial stages.
However, towards the end of our observations, the line strengths are well
simulated with case B model values with electron density n_e = 10^{9-10}
cm^{-3} and a temperature equal to 10^4 K. Based on our distance estimate to
the nova of 5.5 kpc and the observed free-free continuum emission in the later
part of the observations, we estimate the ionized mass of the ejecta to be
between 10^{-5} and 10^{-6} solar-mass.Comment: 10 pages, 8 figures, Accepted for publication in MNRA
Infrared studies of the Be star X Per
Photometric and spectroscopic results are presented for the Be star X Per/HD
24534 from near-infrared monitoring in 2010-2011. The star is one of a sample
of selected Be/X-ray binaries being monitored by us in the near-IR to study
correlations between their X ray and near-IR behaviour. Comparison of the
star's present near-IR magnitudes with earlier records shows the star to be
currently in a prominently bright state with mean J, H, K magnitudes of 5.49,
5.33 and 5.06 respectively. The JHK spectra are dominated by emission lines of
HeI and Paschen and Brackett lines of HI. Lines of OI 1.1287 and 1.3165 micron
are also present and their relative strength indicates, since OI 1.1287 is
stronger among the two lines, that Lyman beta fluorescence plays an important
role in their excitation. Recombination analysis of the HI lines is done which
shows that the Paschen and Brackett line strengths deviate considerably from
case B predictions. These deviations are attributed to the lines being
optically thick and this supposition is verified by calculating the line center
optical depths predicted by recombination theory. Similar calculations indicate
that the Pfund and Humphrey series lines should also be expected to be
optically thick which is found to be consistent with observations reported in
other studies. The spectral energy distribution of the star is constructed and
shown to have an infrared excess. Based on the magnitude of the IR excess,
which is modeled using a free-free contribution from the disc, the electron
density in the disc is estimated and shown to be within the range of values
expected in Be star discs.Comment: Accepted for publication in MNRAS, 7 pages, 6 figure
Geotechnical Effects of the 2015 Magnitude 7.8 Gorkha, Nepal, Earthquake and Aftershocks
This article summarizes the geotechnical effects of the 25 April 2015 M 7.8 Gorkha, Nepal, earthquake and aftershocks, as documented by a reconnaissance team that undertook a broad engineering and scientific assessment of the damage and collected perishable data for future analysis. Brief descriptions are provided of ground shaking, surface fault rupture, landsliding, soil failure, and infrastructure performance. The goal of this reconnaissance effort, led by Geotechnical Extreme Events Reconnaissance, is to learn from earthquakes and mitigate hazards in future earthquakes
Antioxidant Activity of Hawaiian Marine Algae
Marine algae are known to contain a wide variety of bioactive compounds, many of which have commercial applications in pharmaceutical, medical, cosmetic, nutraceutical, food and agricultural industries. Natural antioxidants, found in many algae, are important bioactive compounds that play an important role against various diseases and ageing processes through protection of cells from oxidative damage. In this respect, relatively little is known about the bioactivity of Hawaiian algae that could be a potential natural source of such antioxidants. The total antioxidant activity of organic extracts of 37 algal samples, comprising of 30 species of Hawaiian algae from 27 different genera was determined. The activity was determined by employing the FRAP (Ferric Reducing Antioxidant Power) assays. Of the algae tested, the extract of Turbinaria ornata was found to be the most active. Bioassay-guided fractionation of this extract led to the isolation of a variety of different carotenoids as the active principles. The major bioactive antioxidant compound was identified as the carotenoid fucoxanthin. These results show, for the first time, that numerous Hawaiian algae exhibit significant antioxidant activity, a property that could lead to their application in one of many useful healthcare or related products as well as in chemoprevention of a variety of diseases including cancer
Detection of GRB 090618 with RT-2 Experiment Onboard the Coronas-Photon Satellite
We present the results of an analysis of the prompt gamma-ray emission from
GRB 090618 using the RT-2 Experiment onboard the Coronas-Photon satellite. GRB
090618 shows multiple peaks and a detailed study of the temporal structure as a
function of energy is carried out. As the GRB was incident at an angle of 77
degree to the detector axis, we have generated appropriate response functions
of the detectors to derive the spectrum of this GRB. We have augmented these
results using the publicly available data from the Swift BAT detector and show
that a combined spectral analysis can measure the spectral parameters quite
accurately. We also attempt a spectral and timing analysis of individual peaks
and find evidence for a systematic change in the pulse emission characteristics
for the successive pulses. In particular, we find that the peak energy of the
spectrum, E_p, is found to monotonically decrease with time, for the successive
pulses of this GRB.Comment: 12 pages, 6 figures, 3 tables, Accepted for publication in The
Astrophysical Journa
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Geotechnical Effects of the 2015 Magnitude 7.8 Gorkha, Nepal, Earthquake and Aftershocks
This article summarizes the geotechnical effects of the 25 April 2015 M 7.8 Gorkha, Nepal, earthquake and aftershocks, as documented by a reconnaissance team that undertook a broad engineering and scientific assessment of the damage and collected perishable data for future analysis. Brief descriptions are provided of ground shaking, surface fault rupture, landsliding, soil failure, and infrastructure performance. The goal of this reconnaissance effort, led by Geotechnical Extreme Events Reconnaissance, is to learn from earthquakes and mitigate hazards in future earthquakes.This is the publisher’s final pdf. The published article is copyrighted by Seismological Society of America and can be found at: http://www.seismosoc.org/publications/srl
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