13,746 research outputs found
Complexes of Ag(I), Cu(I), TI(I), Zn(II), Cd(II), Hg(II), Hg(I), Pd(o) & Pt(o) with 2-Thioorotic Acid
884-88
A Study of starless dark cloud LDN 1570: Distance, Dust properties and Magnetic field geometry
We wish to map the magnetic field geometry and to study the dust properties
of the starless cloud, L1570, using multi-wavelength optical polarimetry and
photometry of the stars projected on the cloud. We made R-band imaging
polarimetry of the stars projected on a cloud, L1570, to trace the magnetic
field orientation. We also made multi-wavelength polarimetric and photometric
observations to constrain the properties of dust in L1570. We estimated a
distance of 394 +/- 70 pc to the cloud using 2MASS JHKs colours. Using the
values of the Serkowski parameters namely , ,
{\lambda}max and the position of the stars on near infrared color-color
diagram, we identified 13 stars that could possibly have intrinsic polarization
and/or rotation in their polarization angles. One star, 2MASS
J06075075+1934177, which is a B4Ve spectral type, show the presence of diffuse
interstellar bands in the spectrum apart from showing H{\alpha} line in
emission. There is an indication for the presence of slightly bigger dust
grains towards L1570 on the basis of the dust grain size-indicators such as
{\lambda}max and Rv values. The magnetic field lines are found to be parallel
to the cloud structures seen in the 250{\mu}m images (also in 8{\mu}m and
12{\mu}m shadow images) of L1570. Based on the magnetic field geometry, the
cloud structure and the complex velocity structure, we believe that L1570 is in
the process of formation due to the converging flow material mediated by the
magnetic field lines. Structure function analysis showed that in the L1570
cloud region the large scale magnetic fields are stronger when compared with
the turbulent component of magnetic fields. The estimated magnetic field
strengths suggest that the L1570 cloud region is sub-critical and hence could
be strongly supported by the magnetic field lines.Comment: 26 pages, 22 figures, and 7 tables; Accepted for its publication in
A&
Early time optical spectroscopy of supernova SN 1998S
We present medium-resolution optical spectra of the type II supernova SN 1998S obtained during the pre-maximum, maximum and early decline phases. The early decline spectra show complex Balmer line profiles: a narrow P-Cygni emission feature superimposed on a broad emission. The narrow emission has a redshift similar to that of the host galaxy, indicating its origin from a pre-supernova circumstellar material. The Hα luminosity of the broad component implies a shell mass of ~ 0.1 M☉ for the supernova ejecta, while the luminosity of the narrow component implies a mass loss rate of 10-4M☉ yr-1 for the precursor. The photospheric temperature of the supernova shell decreased from a value of 18400±2900 K on day 17 to a value of 7500±1200 K on day 44. The observations indicate SN 1998S belongs to type IIn supernovae where the supernova ejecta dynamically interact with a pre-supernova circumstellar material
Optical observations of the bright long duration peculiar GRB 021004 afterglow
The CCD magnitudes in Johnson and Cousins and photometric
passbands are determined for the bright long duration GRB 021004 afterglow from
2002 October 4 to 16 starting 3 hours after the ray burst.
Light curves of the afterglow emission in ,, and passbands are
obtained by combining these measurements with other published data. The
earliest optical emission appears to originate in a revese shock. Flux decay of
the afterglow shows a very uncommon variation relative to other well-observed
GRBs. Rapid light variations, especially during early times (
days) is superposed on an underlying broken power law decay typical of a jetted
afterglow. The flux decay constants at early and late times derived from least
square fits to the light curve are and respectively,
with a jet break at around 7 day. Comparison with a standard fireball model
indicates a total extinction of mag in the direction of the
burst. Our low-resolution spectra corrected for this extinction provide a
spectral slope . This value and the flux decay constants
agree well with the electron energy index used in the model. The
derived jet opening angle of about implies a total emitted
gamma-ray energy erg at a cosmological distance
of about 20 Gpc. Multiwavelength observations indicate association of this GRB
with a star forming region, supporting the case for collapsar origin of long
duration GRBs.Comment: 19 pages, 3 figures, BASI, 31, 1
Broad Band Optical Polarimetric Study of IC 1805
We present the BVR broad band polarimetric observations of 51 stars belonging
to the young open cluster IC 1805. Along with the photometric data from the
literature we have modeled and subtracted the foreground dust contribution from
the maximum polarization (P_{max}) and colour excess (E_{B-V}). The mean value
of the P_max for intracluster medium and the foreground are found to be 5.008
+/-0.005 % and 4.865 +/-0.022 % respectively. Moreover, the mean value of the
wavelength of maximum polarization (lambda_{max}) for intracluster medium is
0.541 +/- 0.003 micro m, which is quite similar as the general interstellar
medium (ISM). The resulting intracluster dust component is found to have
negligible polarization efficiency as compared to interstellar dust. Some of
the observed stars in IC 1805 have shown the indication of intrinsic
polarization in their measurements.Comment: 8 pages, 7 figures, Accepted for publication in MNRA
Altered expression of neuroplasticity-related genes in the brain of depressed suicides
Background: Expression of the neuronal membrane glycoprotein M6a (GPM6A), the proteolipid protein (PLP/DM20) family member, is downregulated in the hippocampus of chronically stressed animals. Its neuroplastic function involves a role in neurite formation, filopodium outgrowth and synaptogenesis through an unknown mechanism. Disruptions in neuroplasticity mechanisms have been shown to play a significant part in the etiology of depression. Thus, the current investigation examined whether GPM6A expression is also altered in human depressed brain. Methods: Expression levels and coexpression patterns of GPM6A, GPM6B, and PLP1 (two other members of PLP/DM20 family) as well as of the neuroplasticity-related genes identified to associate with GPM6A were determined using quantitative polymerase chain reaction (qPCR) in postmortem samples from the hippocampus (. n=. 18) and the prefrontal cortex (PFC) (. n=. 25) of depressed suicide victims and compared with control subjects (hippocampus n=. 18; PFC n=. 25). Neuroplasticity-related proteins that form complexes with GPM6A were identified by coimmunoprecipitation technique followed by mass spectrometry. Results: Results indicated transcriptional downregulation of GPM6A and GPM6B in the hippocampus of depressed suicides. The expression level of calcium/calmodulin-dependent protein kinase II alpha (CAMK2A) and coronin1A (CORO1A) was also significantly decreased. Subsequent analysis of coexpression patterns demonstrated coordinated gene expression in the hippocampus and in the PFC indicating that the function of these genes might be coregulated in the human brain. However, in the brain of depressed suicides this coordinated response was disrupted. Conclusions: Disruption of coordinated gene expression as well as abnormalities in GPM6A and GPM6B expression and expression of the components of GPM6A complexes were detected in the brain of depressed suicides.Fil: Fuchsova, Beata. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas ; ArgentinaFil: Alvarez Juliá, Anabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas ; ArgentinaFil: Rizavi, H. S.. University of Illinois; Estados UnidosFil: Frasch, Alberto Carlos C.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas ; ArgentinaFil: Pandey, G. N.. University of Illinois; Estados Unido
Supernovae study: Context of the 4-m ILMT facility
The upcoming 4-m International Liquid Mirror Telescope (ILMT) facility will
perform deep imaging (in single scan 22 mag.) of a narrow strip of
sky each clear night in the Time Delayed Integration mode. A cadence of one day
observation will provide unique opportunities to discover different types of
supernovae (SNe) along with many other types of variable sources. We present
the approach to discover SNe with the ILMT and discuss the follow-up strategy
in the context of other existing observational facilities. The advantages of
the ILMT observations over the traditional glass mirror telescopes are also
discussed.Comment: 8 pages, 3 figures, to appear in proceedings of the First
Belgo-Indian Network for Astronomy & Astrophysics (BINA) Worksho
Star formation in young star cluster NGC 1893
We present a comprehensive multi-wavelength study of the star-forming region
NGC 1893 to explore the effects of massive stars on low-mass star formation.
Using near-infrared colours, slitless spectroscopy and narrow-band
photometry in the cluster region we have identified candidate young stellar
objects (YSOs) distributed in a pattern from the cluster to one of the nearby
nebulae Sim 129. The colour-magnitude diagram of the YSOs indicates
that majority of these objects have ages between 1 to 5 Myr. The spread in the
ages of the YSOs may indicate a non-coeval star formation in the cluster. The
slope of the KLF for the cluster is estimated to be , which agrees
well with the average value () reported for young clusters. For the
entire observed mass range the value of the slope of
the initial mass function, ', comes out to be , which is
in agreement with the Salpeter value of -1.35 in the solar neighborhood.
However, the value of ' for PMS phase stars (mass range ) is found to be which is shallower than the
value () obtained for MS stars having mass range indicating a break in the slope of the mass function at . Estimated ' values indicate an effect of mass segregation
for main-sequence stars, in the sense that massive stars are preferentially
located towards the cluster center. The estimated dynamical evolution time is
found to be greater than the age of the cluster, therefore the observed mass
segregation in the cluster may be the imprint of the star formation process.
There is evidence for triggered star formation in the region, which seems to
govern initial morphology of the cluster.Comment: Accepted for the publication in MNRAS, 21 pages, 26 figures, 10
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