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Near-infrared observations of the Be/X-ray binary pulsar A0535+262

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Research in Astronomy and Astrophysics 2012年第2期12卷 177-186页

作者： Sachindra Naik blesson mathew D.P.K.Banerjee N.M.Ashok Rajeev R.Jaiswal Astronomy and Astrophysics Division Physical Research Laboratory

We present the results obtained from extensive near-infrared （IR） spectro- scopic and photometric observations of the Be/X-ray binary A0535＋262/HDE 245770 at different phases of its - 111 d orbital period. This observation campaign is part of the monitoring program of selective Be/X-ray binary systems aimed at understanding X-ray and near-IR properties at different orbital phases, especially during the perias- tron passage of the neutron star. The near-IR observations presented here were carried out using the 1.2 m telescope at the Mt. Abu IR Observatory. Though the source was relatively faint for spectroscopic observations with the 1.2 m telescope, we monitored the source closely during the 2011 February-March giant X-ray outburst to primarily investigate whether any drastic changes in the near-IR JHK spectra took 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, which could suggest a mild evacuation/truncation of the circumstellar disk 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 μm. The presence of all the 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, suggests that the near- IR line emitting regions of the disk are not significantly affected during the X-ray outburst.

关键词： infrared: stars - Be binaries - stars: individual (A0535+262) - tech-niques: spectroscopic

Discovery of 2716 hot emission-line stars from LAMOST DR5

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Research in Astronomy and Astrophysics 2021年第11期21卷 165-179页

作者： Baskaran Shridharan blesson mathew Sabu Nidhi Ravikumar Anusha Roy Arun Sreeja S.Kartha Yerra Bharat Kumar Department of Physics and Electronics CHRIST(Deemed to be University)Bangalore 560029India Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China

We present a catalog of 3339 hot emission-line stars(ELSs)identified from 451695 O,B and A type spectra,provided by LAMOST Data Release 5(DR5).We developed an automated Python routine that identified 5437 spectra having a peak between 6561 and 6568.False detections and bad spectra were removed,leaving 4138 good emission-line spectra of 3339 unique *** re-estimated the spectral types of 3307 spectra as the LAMOST Stellar Parameter Pipeline(LASP)did not provide accurate spectral types for these emission-line *** Herbig Ae/Be stars exhibit higher excess in near-infrared and mid-infrared wavelengths than classical Ae/Be stars,we relied on 2 MASS and WISE photometry to distinguish ***,we report 1089 classical Be,233 classical Ae and 56 Herbig Ae/Be stars identified from LAMOST *** addition,928 B[em]/A[em]stars and 240 CAe/CBe potential candidates are *** our sample of 3339 hot ELSs,2716 ELSs identified in this work do not have any record in the SIMBAD database and they can be considered as new *** of such a large homogeneous set of emission-line spectra will help the community study the emission phenomenon in detail without worrying about the inherent biases when compiling from various sources.

关键词： stars:early-type methods:data analysis techniques:photometric astronomical databases:catalogs

Studies of a possible new Herbig Ae/Be star in the open cluster NGC 7380

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Research in Astronomy and Astrophysics 2012年第2期12卷 167-176页

作者： blesson mathew D.P.K.Banerjee N.M.Ashok Annapurni Subramaniam Bhaskaran Bhavya Vishal Joshi Astronomy and Astrophysics Division Physical Research LaboratoryNavrangapura Indian Institute of Astrophysics Cochin University of Science and Technology

We present a study of the star 2MASS J22472238＋5801214 with the aim of identifying its true nature which has hitherto been uncertain. This object, which is a member of the young cluster NGC 7380, has been variously proposed to be a Be star, a D-type symbiotic and a Herbig Ae/Be star in separate studies. Here we present optical spectroscopy, near-IR photometry and narrow band Hα imaging of the nebulosity in its environment. Analysis of all these results, including the spectral energy distribution constructed from available data, strongly indicate the source to be a Herbig Ae/Be star. The star is found to be accompanied by a nebulosity with an interesting structure. A bow-shock shaped structure, similar to a cometary nebula, is seen very close to the star with its apex oriented towards the photoionizing source of this region （i.e. the star DH Cep）. An interesting spectroscopic finding, from the forbidden [StI] 6716, 6731A and [OI] 6300A lines, is the detection of a blue-shifted high velocity outflow （200 -t-50 km s-1） from the star.

关键词： stars: emission-line - Be - stars: pre-main sequence -- stars: winds outflows -- galaxies: star clusters: individual: NGC 7380

Optical Spectroscopy of Classical Be Stars in Old Open Clusters

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Research in Astronomy and Astrophysics 2023年第3期23卷 16-24页

作者： Madhu Kashyap Jagadeesh blesson mathew K.T.Paul Gourav Banerjee Suman Bhattacharyya R.Anusha Pramod Kumar S. Department of Physics and Electronics CHRIST(Deemed to be University)Hosur Main RoadBengaluruIndia Department of Physics and Astronomy University of Western OntarioON N6A 3K7Canada Indian Institute of Astrophysics KoramangalaBengaluruIndia

We performed the optical spectroscopy of 16 classical Be stars in 11 open clusters older than 100 *** is the first spectroscopic study of classical Be stars in open clusters older than 100 *** found that the Hαemission strength of most of the stars is less than 40?,in agreement with previous *** analysis further suggests that one of the stars,[KW97]35–12,might be a weak Hαemitter in nature,showing Hαequivalent width of-0.5?.Interestingly,we also found that the newly detected classical Be star LSⅢ+4737b might be a component of the possible visual binary system LSⅢ+4737,where the other companion is also a classical Be ***,the present study indicates the possible detection of a binary Be ***,it is observed that all 16 stars exhibit a lesser number of emission lines compared to classical Be stars younger than 100 ***,the spectral type distribution analysis of B-type and classical Be stars for the selected clusters points out that the existence of CBe stars can depend on the spectral type distribution of B-type stars present in these clusters.

关键词： clusters showing spectroscopic

Optical/IR studies of Be stars in NGC 6834 with emphasis on two specific stars

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Research in Astronomy and Astrophysics 2014年第9期14卷 1173-1192页

作者： blesson mathew Watson P. Varricatt Annapurni Subramaniam N. M. Ashok D. P. K. Banerjee Centre for Astrophysics & Supercomputing Swinburne University Hawthorn VIC 3122Australia Astronomy and Astrophysics Division Physical Research Laboratory NavrangapuraAhmedabad - 380 009 Gujarat India Joint Astronomy Centre 660 N. Aohoku Pl. Hilo HI 96720 USA Indian Institute of Astrophysics Bangalore - 560 034 India

We present optical and infrared photometric and spectroscopic studies of two Be stars in the 70-80-Myr-old open cluster NGC 6834. NGC 6834（1） has been reported as a binary from speckle interferometric studies whereas NGC 6834（2） may possibly be a γ Cas-like variable. Infrared photometry and spectroscopy from the United Kingdom Infrared Telescope （UKIRT）, and optical data from various facilities are combined with archival data to understand the nature of these candidates. High signal-to-noise near-IR spectra obtained from UKIRT have enabled us to study the optical depth effects in the hydrogen emission lines of these stars. We have explored the spectral classification scheme based on the intensity of emission lines in the H and K bands and contrasted it with the conventional classification based on the intensity of hydrogen and helium absorption lines. This work also presents hitherto unavailable UBV CCD photometry of NGC 6834, from which the evolutionary state of the Be stars is identified.

关键词： stars: emission-line Be -- circumstellar matter -- infrared: stars -- line profiles -- (Galaxy:) open clusters and associations: individual (NGC 6834)

Spectroscopic Study of Late-type Emission-line Stars Using the Data from LAMOST DR6

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Research in Astronomy and Astrophysics 2024年第12期 140-157页

作者： D.Edwin blesson mathew B.Shridharan Vineeth Valsan S.Nidhi Suman Bhattacharyya Sreeja S.Kartha T.Robin Department of Physics and Electronics CHRIST (Deemed to be University) Department of Astronomy and Astrophysics Tata Institute of Fundamental Research The Oxford College of Science

Low-mass emission-line stars belong to various evolutionary stages, from pre-main-sequence young stars to evolved stars. In this work, we present a catalog of late-type (F0 to M9) emission-line stars from the LAMOST Data Release 6. Using the scipy package, we created a Python code that finds the emission peak at Hα in all latetype stellar spectra. A data set of 38,152 late-type emission-line stars was obtained after a rigorous examination of the photometric quality flags and the signal-to-noise ratio of the spectra. Adopting well-known photometric and spectroscopic methods, we classified our sample into 438 infrared (IR) excess sources, 4669 post-main-sequence candidates, 9718 Fe/Ge/Ke sources, and 23,264 d Me sources. From a crossmatch with known databases, we found that 29,222 sources, comprising 65 IR excess sources, 7899 Fe/Ge/Ke stars, 17,533 dMe stars, and3725 PtMS candidates, are new detections. We measured the equivalent width of the major emission lines observed in the spectra of our sample of emission-line stars. Furthermore, the trend observed in the line strengths of major emission lines over the entire late-type spectral range is analyzed. We further classified the sample into four groups based on the presence of hydrogen and calcium emission lines. This work presents a large data set of late-type emission-line stars, which can be used to study active phenomena in late-type stars.

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Maternal low protein diet and fetal programming of lean type 2 diabetes

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World Journal of Diabetes 2022年第3期13卷 185-202页

作者： Vidyadharan Alukkal Vipin Chellakkan Selvanesan blesson Chandra Yallampalli Department of Obstetrics and Gynecology Baylor College of MedicineHoustonTX 77030United States Family Fertility Center Texas Children's HospitalHoustonTX 77030United States

Maternal nutrition is found to be the key factor that determines fetal health in utero and metabolic health during *** diseases have been primarily attributed to impaired maternal nutrition during pregnancy,and impaired nutrition has been an immense issue across the *** recent years,type 2 diabetes(T2D)has reached epidemic proportion and is a severe public health problem in many *** plenty of research has already been conducted to tackle T2D which is associated with obesity,little is known regarding the etiology and pathophysiology of lean T2D,a variant of *** studies have focused on the effects of epigenetic variation on the contribution of in utero origins of lean T2D,although other mechanisms might also contribute to the *** studies in humans and experiments in animals strongly suggest an association between maternal low protein diet and lean T2D *** addition,clear sex-specific disease prevalence was observed in different ***,more research is essential for the understanding of the etiology and pathophysiology of lean T2D,which might help to develop better disease prevention and treatment *** review examines the role of protein insufficiency in the maternal diet as the central driver of the developmental programming of lean T2D.

关键词： Type 2 diabetes Maternal low protein diet Fetal programming Lean diabetes Developmental origin of health and disease

Two Stream Instability as a Source of Coronal Heating

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International Journal of Astronomy and Astrophysics 2015年第2期5卷 61-69页

作者： Antony Soosaleon blesson Jose SPAP Mahatma Gandhi University Kottayam India

Recent observation of oscillating the two stream instability (TSI) in a solar type III radio bursts and spatial damping of Langmuir oscillations has made this instability as an important candidate to understand the coronal heating problem. This instability has been studied by several authors for cold plasma found to be stable for high frequencies (greater than plasma frequency ωp). In this paper, we prove that this instability is unstable for warm plasma for higher frequencies (greater than plasma frequency ωp) and much suitable to study the solar coronal heating problem. We have derived a general dispersion relation for warm plasma and discussed the various methods analyzing the instability conditions. Also, we derived an expression for the growth rate of TSI and analyzed the growth rate for photospheric and coronal plasmas. A very promising result is that the ion temperature is the source of this instability and shifts the growth rate to high frequency region, while the electron temperature does the reverse. TSI shows a high growth rate for a wide frequency range for photosphere plasma, suggesting that the electron precipitation by magnetic reconnection current, acceleration by flares, may be source of TSI in the photosphere. But for corona, these waves are damped to accelerate the ions and further growing of such instability is prohibited due to the high conductivity in coronal plasma. The TSI is a common instability;the theory can be easily modifiable for multi-ion plasmas and will be a useful tool to analyze all the astrophysical problems and industrial devices, too.

关键词： Coronal Heating Two Stream Instability Langmuir Waves Ion Temperature Drift Velocity Photosphere Fusion Plasma

Effects of selective estrogen receptor agonists on estrogen receptor expression in the uterus of ovariectomized rats

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Open Journal of Molecular and Integrative Physiology 2012年第2期2卷 35-43页

作者： C. S. blesson Britt Masironi Lena Sahlin Division for Reproductive Endocrinology and the Pediatric Endocrinology Unit Department of Women’s and Children’s Health Karolinska Institutet Stockholm Sweden

The aim of the present study was to investigate effects of short time treatment with estrogen receptor (ER) selective agonists on ERα, ERβ and G-protein coupled estrogen receptor-1 (GPER) expression in the uterus of ovariectomized rats. The rats were treated with either estradiol (E2), the specific ERα agonist PPT or the specific ERβ agonist DPN for 18 hrs. Uterine weights were higher after E2 or PPT treatment than after DPN or no treatment. ERα mRNA levels decreased significantly in PPT and DPN treated animals as compared to controls. Stromal ERα immunostaining was higher after E2 treatment than in controls. The ERβ mRNA level was lower in the E2 and PPT groups compared with controls. ERβ immunoreactivity was higher in the myometrium after DPN treatment than in controls. The GPER mRNA level was lower in the E2 and DPN groups as compared to the controls, whereas total protein levels did not display any change. The proliferation marker Ki-67 increased after PPT treatment in stroma and myometrium, as compared to controls. Thus, uterine growth and proliferation are predominately regulated via ERα. Also ERβ expression showed regulation via ERα, while GPER expression indicated control via ERβ. This short term treatment did not result in any regulation of the total protein level as determined by Western blot. However, treatment by E2 increased ERα immunostaining in the stroma and DPN augmented ERβ immunostaining in the myometrium. Thus, the estrogen receptors in the rat uterus are differently regulated depending on the ligand and tissue type.

关键词： PPT DPN ERα ERβ GPER