15 research outputs found
HI line analysis of Herbig Ae/Be stars using X-Shooter spectra
Herbig Ae/Be stars are intermediate-mass pre-main sequence stars undergoing
accretion through their circumstellar disk. The optical and infrared (IR)
spectra of HAeBe stars show HI emission lines belonging to Balmer, Paschen and
Brackett series. We use the archival X-Shooter spectra available for 109 HAeBe
stars from Vioque et al. (2018) and analyse the various HI lines present in
them. We segregated the stars into different classes based on the presence of
higher-order lines in different HI series. We discuss the dependence of the
appearance of higher-order lines on the stellar parameters. We find that most
massive and younger stars show all the higher-order lines in emission. The
stars showing only lower-order lines have Teff < 12000 K and an age range of
5-10 Myr. We perform a Case B line ratio analysis for a sub-sample of stars
showing most of the HI lines in emission. We note that all but four stars
belonging to the sub-sample show lower HI line ratios than theoretical values,
owing to the emitting medium being optically thick. The HI line flux ratios do
not depend on the star's spectral type. Further, from the line ratios of
lower-order lines and Paschen higher-order lines, we note that line ratios of
most HAeBe stars match with electron density value in the range 10^9 - 10^11
cm^-3. The electron temperature, however, could not be ascertained with
confidence using the line ratios studied in this work.Comment: Accepted, To be published as part of the JOAA special issue on "3rd
Meeting on Star Formation: Star Formation Studies in the Context of NIR
Instruments on 3.6m DOT". 12 pages, 7 figure
Spectroscopic study of Herbig Ae/Be stars in the Galactic Anti-center region from LAMOST DR5
We study a sample of 119 Herbig Ae/Be stars in the Galactic anti-center
direction using the spectroscopic data from Large sky Area Multi-Object fiber
Spectroscopic Telescope (LAMOST) survey program. Emission lines of hydrogen
belonging to the Balmer and Paschen series, and metallic lines of species such
as FeII, OI, CaII triplet are identified. A moderate correlation is observed
between the emission strengths of H and FeII 5169 \r{A}, suggesting a
possible common emission region for FeII lines and one of the components of
H. We explored a technique for the extinction correction of the HAeBe
stars using diffuse interstellar bands present in the spectrum. We estimated
the stellar parameters such as age and mass of these HAeBe stars, which are
found to be in the range 0.1 -- 10 Myr and 1.5 -- 10 , respectively.
We found that the mass accretion rate of the HAeBe stars in the Galactic
anti-center direction follows the relation
, which is similar to the relation derived for
HAeBe stars in other regions of the Galaxy. The mass accretion rate of HAeBe
stars is found to have a functional form of with age, in agreement with previous studies.Comment: 18 pages, 11 figures, 3 tables, accepted for publication in MNRA
Equatorial and low latitude ionosphere thermosphere interactions
Over the recent years the equational and low latitude phenomena in the upper atmosphere have been drawing the attention of Aeronomers and space scientists world-wide. The equatorial region reveals a variety of geophysical phenomena which are perfect examples for the neutral atmosphere and the F-region of the ionosphere to behave as a closely coupled system. The present paper is an overview of these interactive processes and our current understanding and it also touches upon the grey areas which call for a concerted investigation
Stationary and nonstationary iterative methods for nonlinear boundary value problems
Mathematical and Computer Modelling18243-62MCMO
Fullerenes in the circumstellar medium of Herbig Ae/Be stars: Insights from the Spitzer mid-infrared spectral catalog
This study presents the largest mid-infrared spectral catalog of Herbig Ae/Be
stars to date, containing the Spitzer Infrared Spectrograph spectra of 126
stars. Based on the catalog analysis, two prominent infrared vibrational modes
of C\textsubscript{60} bands at 17.4 and 18.9 are detected in
the spectra of nine sources, while 7.0 feature is identified in the
spectra of HD 319896. The spectral index analysis and the comparison of the
known sources with C\textsubscript{60} features indicated that there exist two
different types of emission classes among the sample of stars. The infrared
spectra of six Herbig Ae/Be stars in this study resemble that of reflection
nebulae, and their association with previously known reflection nebulae is
confirmed. In the case of three Herbig Ae/Be stars we report the tentative
evidence of C\textsubscript{60} emission features originating from the
circumstellar disk or nearby diffused emission region. The detection fraction
of C\textsubscript{60} in the total HAeBe star sample is 7\%, whereas
the detection fraction is 30\% for HAeBe stars associated with nebulosity. In
the catalog, C\textsubscript{60} is exclusively present in the circumstellar
regions of B type Herbig Ae/Be stars, with no evidence of its presence detected
in stars with later spectral types. The present study has increased the number
of young stellar objects and reflection nebulae detected with
C\textsubscript{60} multifold, which can help in understanding the excitation
and formation pathway of the species.Comment: 14 pages,2 tables, 6 figures, accepted for publication in MNRA
Endoplasmic reticulum targeted chemotherapeutics: the remarkable photo-cytotoxicity of an oxovanadium(iv) vitamin-B6 complex in visible light (vol 50, pg 5590, 2014)
Correction for `Endoplasmic reticulum targeted chemotherapeutics: the remarkable photo-cytotoxicity of an oxovanadium(iv) vitamin-B6 complex in visible light' by Samya Banerjee et al., Chem. Commun., 2014, 50, 5590-5592
Endoplasmic reticulum targeted chemotherapeutics: the remarkable photo-cytotoxicity of an oxovanadium(IV) vitamin-B6 complex in visible light
An oxovanadium(IV) vitamin-B6 Schiff base complex, viz. VO(HL)( acdppz)] Cl, having (acridinyl) dipyridophenazine (acdppz) shows specific localization to endoplasmic reticulum (ER) and remarkable apoptotic photocytotoxicity in visible light (400-700 nm) in HeLa and MCF-7 cancer cells (IC50 < 0.6 mu M) while being non-toxic in the dark and to MCF-10A normal cells (IC50 > 40 mu M)
Emission line star catalogues post-
Aims.Gaia Data Release 3 (DR3) and further releases have the potential to identify and categorise new emission-line stars in the Galaxy. We perform a comprehensive validation of astrophysical parameters from Gaia DR3 with the spectroscopically estimated emission-line star parameters from the LAMOST OBA emission catalogue.
Method. We compare different astrophysical parameters provided by Gaia DR3 with those estimated using LAMOST spectra. By using a larger sample of emission-line stars, we performed a global polynomial and piece-wise linear fit to update the empirical relation to convert the Gaia DR3 pseudo-equivalent width to the observed equivalent width, after removing the weak emitters from the analysis.
Results. We find that the emission-line source classifications given by DR3 is in reasonable agreement with the classification from the LAMOST OBA emission catalogue. The astrophysical parameters estimated by the esph