• BLESSON MATHEW

      Articles written in Journal of Astrophysics and Astronomy

    • Quasar catalogue for the astrometric calibration of the forthcoming ILMT survey

      AMIT KUMAR MANDAL BIKRAM PRADHAN JEAN SURDEJ C. S. STALIN RAM SAGAR BLESSON MATHEW

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      Quasars are ideal targets to use for astrometric calibration of large scale astronomical surveys as they have negligible proper motion and parallax. The forthcoming 4-m International Liquid Mirror Telescope (ILMT) will survey the sky that covers a width of about 27$'$. To carry out astrometric calibration of theILMT observations, we aimed to compile a list of quasars with accurate equatorial coordinates and falling in the ILMT stripe. Towards this, we cross-correlated all the quasars that are known till the present date with the sources in the Gaia-DR2 catalogue, as the Gaia-DR2 sources have position uncertainties as small as a few milli arcsec (mas). We present here the results of this cross-correlation which is a catalogue of 6738 quasars that is suitable for astrometric calibration of the ILMT fields. In this work, we present this quasar catalogue. This catalogue of quasars can also be used to study quasar variability over diverse time scales when the ILMT starts its observations. While preparing this catalogue, we also confirmed that quasars in the ILMT stripe have proper motion and parallax lesser than 20 mas yr$^{-1}$ and 10 mas, respectively.

    • Study of classical Be stars in open clusters older than 100 Myr

      MADHU KASHYAP JAGADEESH BLESSON MATHEW K. T. PAUL GOURAV BANERJEE ANNAPURNI SUBRAMANIAM R. ARUN

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      We performed the slitless spectroscopic survey to identify classical Be (CBe) stars in openclusters older than 100 Myr. Observing a sample of 71 open clusters, we identified 13 CBe stars in 11 open clusters, one of, which (TYC 2679-432-1) is a new detection. The 13 CBe stars show both H$\alpha$ in emission and IR excess, which confirm that they possess gaseous circumstellar discs. Two more CBe stars are found toexhibit H$\alpha$ in absorption for the first time, indicating that might be passing through disc-less episode presently. The spectral-type estimation is done for all these 15 stars and it is noticed that they belong to B0.5–B8 type. Moreover, we found that the distribution of our sample is peaking near late B-types as expected.

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