http://hdl.handle.net/2248/8461 2026-04-14T19:57:37Z 2026-04-14T19:57:37Z Parthasarathy, M http://hdl.handle.net/2248/8631 2025-01-09T04:21:43Z 2024-12-01T00:00:00Z

Title: Analysis of Gaia DR3 data of selected R Stars (warm carbon stars) Authors: Parthasarathy, M Abstract: An analysis of Gaia DR3 data of 67 R stars is presented and 57 of them are at high galactic latitudes. Three new variable stars are found. The long period luminous variable R stars and R8 stars may be variable carbon stars on the AGB. The R stars seem to have luminosities throughout the RGB range. Several R stars are found to be high velocity stars. The determination of s-process elements abundances and C12/C13 ratio of the stars listed in Table 1 will enable us to further understand the R stars phenomenon. The process by which the atmospheres of these stars are enriched with carbon is still a puzzle. Description: Open Access; Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI

2024-12-01T00:00:00Z Singh, Saikhom Pravash Archana Soam http://hdl.handle.net/2248/8569 2024-11-07T06:22:01Z 2024-09-01T00:00:00Z

Title: Dust grain properties in extragalactic environment through supernovae dust polarisation observations Authors: Singh, Saikhom Pravash; Archana Soam Abstract: Dust polarisation observations of starlight at multi-wavelengths helps us to find maximum polari6 sation, Pmax and the corresponding wavelength, λmax. This λmax is approximately proportional to 7 average grain size, thereby helping to reveal grain sizes in the intervening medium. We study the 8 average grain sizes in different host galaxies of 4 Type Ia and 10 Type II supernovae through spec9 tropolarimetric observations at multi wavelengths and compare with the average grain sizes in the 10 diffused interstellar medium of our galaxy. We use archival Pmax, λmax and width of peak of polari11 sation curve (K) values from the literature. We plot Pmax versus λmax in color scale that represents 12 K and find that grain sizes of some of the galaxies are smaller, some nearly comparable and some 13 larger than typical grain size (≈ 5500˚A) of our galaxy. This gives us an insight into the different grain 14 properties especially their sizes in external galaxies compared to our galaxy. Description: Open Access; Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI

2024-09-01T00:00:00Z Parthasarathy, M http://hdl.handle.net/2248/8525 2024-09-03T04:16:13Z 2024-07-01T00:00:00Z

Title: Analysis of Gaia DR3 data of selected high galactic latitude H-alpha emission stars Authors: Parthasarathy, M Abstract: Gaia DR3 data of 52 high galactic latitude Hα emission stars selected from the paper of Stephenson are analyzed. Ten new variable stars and eight new high velocity stars have been found. Details of six post-AGB stars and several other interesting stars are discussed. Many of the stars presented in this paper have Gaia DR3 light curves and spectra. A detailed study of these 52 stars is needed to derive their chemical composition and to further understand their binarity, circumstellar matter and evolutionary status. The astrophysical parameters from the Gaia DR3 data reveal several hot (OBA) and several F and G-type stars in this sample. Some of them are metal-poor stars. Description: Open Access; Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

2024-07-01T00:00:00Z Parthasarathy, M http://hdl.handle.net/2248/8502 2024-07-08T09:19:09Z 2024-06-01T00:00:00Z

Title: Gaia DR3 Data of Very Young Open Cluster NGC 6530: Distance and Evolutionary Stage of Selected Stars Authors: Parthasarathy, M Abstract: Gaia EDR3 and Gaia DR3 data of selected stars in the very young (1.5-million-year-old) open cluster NGC 6530 are presented. All the selected stars have very accurate Gaia DR3 distances. Most of the selected stars are very young B stars and several of them are young stellar objects (YSO). From the analysis of selected stars, the distance to NGC 6530 is found to be 1318 pc. The two very red stars VAJ 304 and 338 have little bit less proper motion than other members of the NGC 6530 and their Mv values are found to be -3.57 and -3.68 respectively. They are much brighter than K5 III RGB stars and less luminous than massive K5 red supergiants. It is likely VAJ 304 and VAJ 338 are not members of NGC 6530 they may be field K5 type AGB or postAGB stars. Further study of these two stars is needed. Description: Open Access; Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

2024-06-01T00:00:00Z