14 research outputs found
Pre-main-sequence population in NGC 1893 region
In this paper we continued our efforts to understand the star formation
scenario in and around the young cluster NGC 1893. We used a sample of the
young stellar sources (YSOs) identified on the basis of multiwavelength data
(optical, near-infrared (NIR), mid-infrared (MIR) and X-ray) to study the
nature of YSOs associated with the region. The identified YSOs show an age
spread of ~ 5 Myr. The YSOs located near the nebulae at the periphery of the
cluster are relatively younger in comparison to those located within the
cluster region. The present results are in accordance with those obtained by us
in previous studies. Other main results from the present study are: 1) the
fraction of disk bearing stars increases towards the periphery of the cluster;
2) there is an evidence supporting the notion that the mechanisms for disk
dispersal operate less efficiently for low-mass stars; 3) the sample of Class
II sources is found to be relatively older in comparison to that of Class III
sources. A comparison of various properties of YSOs in the NGC 1893 region with
those in the Tr 37/ IC 1396 region is also discussed.Comment: Accepted for publication in New Astronom
Host galaxy magnitude of OJ 287 from its colours at minimum light
OJ 287 is a BL Lacertae type quasar in which the active galactic nucleus (AGN) outshines the host galaxy by an order of magnitude. The only exception to this may be at minimum light when the AGN activity is so low that the host galaxy may make quite a considerable contribution to the photometric intensity of the source. Such a dip or a fade in the intensity of OJ 287 occurred in 2017 November, when its brightness was about 1.75 mag lower than the recent mean level. We compare the observations of this fade with similar fades in OJ 287 observed earlier in 1989, 1999, and 2010. It appears that there is a relatively strong reddening of the B-V colours of OJ 287 when its V-band brightness drops below magnitude 17. Similar changes are also seen in V-R, V-I, and R-I colours during these deep fades. These data support the conclusion that the total magnitude of the host galaxy is V = 18.0 ± 0.3, corresponding to MK =-26.5 ± 0.3 in the K-band. This is in agreement with the results, obtained using the integrated surface brightness method, from recent surface photometry of the host. These results should encourage us to use the colour separation method also in other host galaxies with strongly variable AGN. In the case of OJ 287, both the host galaxy and its central black hole are among the biggest known, and its position in the black hole mass-galaxy mass diagram lies close to the mean correlation
Not Available
Not AvailableExtent of Linkage among Scientists, Extension Personnel and Fish Farmers in Tripura, IndiaNot Availabl