arXiv subjects

J. P. Ninan

Publications and source records attributed to J. P. Ninan.

25 records · Page 2Linked to original sources

arXiv2015

V899 Mon: An Outbursting Protostar With Peculiar Light Curve And Its Transition Phases

We present a detailed study of V899 Mon (a new member in the FUors/EXors family of young low-mass stars undergoing outburst), based on our long-term monitoring of the source starting from November 2009 to April 2015. Our optical and near-infrared photometric and spectroscopic monitoring recorded the source transitioning from its first outburst to a short duration quiescence phase ($<$ 1 year), and then returning to a second outburst. We report here the evolution of the outflows from inner region of the disk as the accretion rate evolved in various epochs. Our high resolution (R$\sim$37000) optical spectrum could resolve interesting clumpy structures in the outflow traced by various lines. Change in far-infrared flux was also detected between two outburst epochs. Based on our observations we constrained various stellar and envelope parameters of V899 Mon, as well as the kinematics of its accretion and outflow. The photometric and spectroscopic properties of this source fall between classical FUors and EXors. Our investigation of V899 Mon hints instability associated with magnetospheric accretion to be the physical cause of sudden short duration pause of outburst in 2011. It is also a good candidate to explain similar short duration pauses in outburst of some other FUors/EXors sources.

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arXiv2015

Sh2-138: Physical environment around a small cluster of massive stars

We present a multi-wavelength study of the Sh2-138, a Galactic compact H II region. The data comprise of optical and near-infrared (NIR) photometric and spectroscopic observations from the 2-m Himalayan Chandra Telescope, radio observations from the Giant Metrewave Radio Telescope (GMRT), and archival data covering radio through NIR wavelengths. A total of 10 Class I and 54 Class II young stellar objects (YSOs) are identified in a 4'.6$\times$4'.6 area of the Sh2-138 region. Five compact ionized clumps, with four lacking of any optical or NIR counterparts, are identified using the 1280 MHz radio map, and correspond to sources with spectral type earlier than B0.5. Free-free emission spectral energy distribution fitting of the central compact H II region yields an electron density of ~2250$\pm$400 cm$^{-3}$. With the aid of a wide range of spectra, from 0.5-15 $μm$, the central brightest source - previously hypothesised to be the main ionizing source - is characterized as a Herbig Be type star. At large scale (15'$\times$15'), the Herschel images (70-500 $μm$) and the nearest neighbour analysis of YSOs suggest the formation of an isolated cluster at the junction of filaments. Furthermore, using a greybody fit to the dust spectrum, the cluster is found to be associated with the highest column density (~3$\times$10$^{22}$ cm$^{-2}$) and high temperature (~35 K) regime, as well as with the radio continuum emission. The mass of the central clump seen in the column density map is estimated to be ~3770 $M_\odot$.

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arXiv2014

TIRSPEC : TIFR Near Infrared Spectrometer and Imager

We describe the TIFR Near Infrared Spectrometer and Imager (TIRSPEC) designed and built in collaboration with M/s. Mauna Kea Infrared LLC, Hawaii, USA, now in operation on the side port of the 2-m Himalayan Chandra Telescope (HCT), Hanle (Ladakh), India at an altitude of 4500 meters above mean sea level. The TIRSPEC provides for various modes of operation which include photometry with broad and narrow band filters, spectrometry in single order mode with long slits of 300" length and different widths, with order sorter filters in the Y, J, H and K bands and a grism as the dispersing element as well as a cross dispersed mode to give a coverage of 1.0 to 2.5 microns at a resolving power R of ~1200. The TIRSPEC uses a Teledyne 1024 x 1024 pixel Hawaii-1 PACE array detector with a cutoff wavelength of 2.5 microns and on HCT, provides a field of view of 307" x 307" with a plate scale of 0.3"/pixel. The TIRSPEC was successfully commissioned in June 2013 and the subsequent characterization and astronomical observations are presented here. The TIRSPEC has been made available to the worldwide astronomical community for science observations from May 2014.

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arXiv2013

Re-appearance of McNeil's nebula (V1647 Orionis) and its outburst environment

We present a detailed study of McNeil's nebula (V1647 Ori) in its ongoing outburst phase starting from September 2008 to March 2013. Our 124 nights of photometric observations were carried out in optical V, R, I and near-infrared J, H, K bands, and 59 nights of medium resolution spectroscopic observations were done in 5200 - 9000 Ang wavelength range. All observations were carried out with 2-m Himalayan Chandra Telescope and 2-m IUCAA Girawali Telescope. Our observations show that over last four and a half years, V1647 Ori and the region C near Herbig-Haro object, HH 22A, have been undergoing a slow dimming at a rate of ~0.04 mag/yr and ~0.05 mag/yr respectively in R-band, which is 6 times slower than the rate during similar stage of V1647 Ori in 2003 outburst. We detected change in flux distribution over the reflection nebula implying changes in circumstellar matter distribution between 2003 and 2008 outbursts. Apart from steady wind of velocity ~350 km/s we detected two episodic magnetic reconnection driven winds. Forbidden [O I] 6300 Ang and [Fe II] 7155 Ang lines were also detected implying shock regions probably from jets. We tried to explain the outburst timescales of V1647 Ori using the standard models of FUors kind of outburst and found that pure thermal instability models like Bell & Lin (1994) cannot explain the variations in timescales. In the framework of various instability models we conclude that one possible reason for sudden ending of 2003 outburst in 2005 November was due to a low density region or gap in the inner region (~ 1 AU) of the disc.

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arXiv2013

Large-scale mapping of the massive star-forming region RCW38 in the [CII] and PAH emission

We investigate the large-scale structure of the interstellar medium (ISM) around the massive star cluster RCW38 in the [CII] 158 um line and polycyclic aromatic hydrocarbon (PAH) emission. We carried out [CII] line mapping of an area of ~30'x15' for RCW~38 by a Fabry-Perot spectrometer on a 100 cm balloon-borne telescope with an angular resolution of ~1'.5. We compared the [CII] intensity map with the PAH and dust emission maps obtained by the AKARI satellite. The [CII] emission shows a highly nonuniform distribution around the cluster, exhibiting the structure widely extended to the north and the east from the center. The [CII] intensity rapidly drops toward the southwest direction, where a CO cloud appears to dominate. We decompose the 3-160 um spectral energy distributions of the surrounding ISM structure into PAH as well as warm and cool dust components with the help of 2.5-5 um spectra. We find that the [CII] emission spatially corresponds to the PAH emission better than to the dust emission, confirming the relative importance of PAHs for photo-electric heating of gas in photo-dissociation regions. A naive interpretation based on our observational results indicates that molecular clouds associated with RCW38 are located both on the side of and behind the cluster.

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arXiv2012

TIRCAM2: The TIFR Near Infrared Imaging Camera

TIRCAM2 (TIFR Near Infrared Imaging Camera - II) is a closed cycle cooled imager that has been developed by the Infrared Astronomy Group at the Tata Institute of Fundamental Research for observations in the near infrared band of 1 to 3.7 microns with existing Indian telescopes. In this paper, we describe some of the technical details of TIRCAM2 and report its observing capabilities, measured performance and limiting magnitudes with the 2-m IUCAA Girawali telescope and the 1.2-m PRL Gurushikhar telescope. The main highlight is the camera's capability of observing in the nbL (3.59 microns) band enabling our primary motivation of mapping of Polycyclic Aromatic Hydrocarbon (PAH) emission at 3.3 microns.

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arXiv2012

The outburst and nature of young eruptive low mass stars in dark clouds

The FU Orionis (FUor) or EX Orionis (EXor) phenomenon has attracted increasing attention in recent years and is now accepted as a crucial element in the early evolution of low-mass stars. FUor and EXor eruptions of young stellar objects (YSOs) are caused by strongly enhanced accretion from the surrounding disk. FUors display optical outbursts of $\sim$ 4 mag or more and last for several decades, whereas EXors show smaller outbursts ($Δ$m $\sim$ 2 - 3 mag) that last from a few months to a few years and may occur repeatedly. Therefore, FUor/EXor eruptions represent a rare but very important phenomenon in early stellar evolution, during which a young low-mass YSO brightens by up to several optical magnitudes. Hence, long-term observations of this class of eruptive variable are important to design theoretical models of low-mass star formation. In this paper, we present recent results from our long-term monitoring observations of three rare types of eruptive young variables with the 2-m Himalayan {\it Chandra} Telescope (HCT) and the 2-m IUCAA Girawali Observatory (IGO) telescope.

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