NGC 7419: A young open cluster with a number of very young intermediate mass pre-MS stars

We present a photometric and spectroscopic study of the young open cluster NGC 7419, which is know to host a large number of classical Be stars for reasons not well understood. Based on CCD photometric observations of 327 stars in UBV passbands, we estimated the cluster parameters as, reddening E(B-V) = 1.65 +/- 0.15 mag and distance = 2900 +/- 400 pc. The turn off age of the cluster was estimated as 25 +/- 5 Myr using isochrone fits. UBV data of the stars were combined with JHK data from 2MASS and were used to create the near infrared (NIR) (J-H) vs (H-K) colour-colour diagram. A large fraction of stars (42%) was found to have NIR excess and their location in the diagram was used to identify them as intermediate mass pre-MS stars. The isochrone fits to pre-MS stars in the optical colour-magnitude diagram showed that the turn-on age of the cluster is 0.3 - 3 Myr. This indicates that there has been a recent episode of star formation in the vicinity of the cluster. Slit-less spectra were used to identify 27 stars which showed H-alpha in emission in the field of the cluster, of which 6 are new identifications. All these stars were found to show NIR excess and located closer to the region populated by Herbig Ae/Be stars in the (J-H) vs (H-K) diagram. Slit spectra of 25 stars were obtained in the region 3700A - 9000A. The spectral features were found to be very similar to those of Herbig Be stars. Those stars were found to be more reddened than the main sequence stars by 0.4 mag on an average. Thus the emission line stars found in this cluster are more similar to the Herbig Be type stars where the circumstellar material is the remnant of the accretion disk.Comment: 20 pages, 11 figures, Accepted for publishing in MNRAS on April 19, 200

Discovery of a possible symbiotic binary in the Large Magellanic Cloud

We report the discovery of a possible symbiotic star, in the Large Magellanic Cloud (LMC). The object under consideration here, designated as RP 870, was detected during the course of a comprehensive H$\alpha$ survey of the LMC by Reid & Parker (2012). The spectrum of RP 870 showed high ionization emission lines of He I, He II and [O III] and molecular absorption bands of TiO $\lambda$$\lambda$6180, 7100. The collective signatures of a hot component (high excitation/ionization lines) and of a cool component (TiO molecular bands) are seen in RP 870, from which we propose it as a symbiotic star. Since known symbiotic systems are rare in the LMC, possibly less than a dozen are known, we thought the present detection to be interesting enough to be reported.Comment: 3 pages, 2 figures, accepted for publication in Research Notes of the AA

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

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 gamma 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.Comment: Published in Research in Astronomy and Astrophysics, RAA 14 (2014) 1173-1192, 20 pages, 10 figure

Determination of the size of the dust torus in H0507+164 through optical and infrared monitoring

The time delay between flux variations in different wavelength bands can be used to probe the inner regions of active galactic nuclei (AGN). Here, we present the first measurements of the time delay between optical and near-infrared (NIR) flux variations in H0507+164, a nearby Seyfert 1.5 galaxy at z = 0.018. The observations in the optical V -band and NIR J, H and Ks bands carried over 35 epochs during the period October 2016 to April 2017 were used to estimate the inner radius of the dusty torus. From a careful reduction and analysis of the data using cross-correlation techniques, we found delayed responses of the J, H and Ks light curves to the V -band light curve. In the rest frame of the source, the lags between optical and NIR bands are found to be $27.1^{+13.5}_{-12.0}$ days (V vs. J), $30.4^{+13.9}_{-12.0}$ days (V vs. H) and $34.6^{+12.1}_{-9.6}$ days (V vs. K ). The lags between the optical and different NIR bands are thus consistent with each other. The measured lags indicate that the inner edge of dust torus is located at a distance of 0.029 pc from the central UV/optical AGN continuum. This is larger than the radius of the broad line region of this object determined from spectroscopic monitoring observations thereby supporting the unification model of AGN. The location of H0507+164 in the {\tau} - MV plane indicates that our results are in excellent agreement with the now known lag-luminosity scaling relationship for dust in AGN.Comment: 8 pages, 4 figures, accepted by MNRAS main journa

Near-infrared Observations of Be/X-ray Binary Pulsar A0535+262

We present results obtained from an extensive near-infrared spectroscopic and photometric observations of the Be/X-ray binary A0535+262/HDE 245770 at different phases of its ~111 day orbital period. This observation campaign is a part of the monitoring programme of selective Be/X-ray binary systems aimed at understanding the X-ray and near-IR properties at different orbital phases, especially during the periastron passage of the neutron star. The near-IR observations were carried out using the 1.2 m telescope at Mt. Abu IR observatory. Though the source was relatively faint for spectroscopic observations with 1.2 m telescope, we monitored the source during the 2011 February--March giant outburst to primarily investigate whether any drastic changes in the near-IR JHK spectra take 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 that could suggest a mild evacuation/truncation of the circumstellar disc 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 micron. The presence of all 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 suggest that the near-IR line emitting regions of the disc are not significantly affected during the X-ray outburst.Comment: 10 Pages, 5 Figures, Accepted for publication in Res. in Astronomy and Astrophysic