IGO Publications

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Start date: 2001

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    Design and development of an optical-fibre-based Integral Field Unit (IFU) on the IUCAA 2-m telescope
    (Mon. Not. R. Astron. Soc., 2011-07-31) Srivastava, Mudit K.; Ramaprakash, A.N.; Das, H.K.
    An optical-fibre-based Integral Field Unit (IFU) has been developed for the Inter-University Centre for Astronomy and Astrophysics (IUCAA) Faint Object Spectrometer and Camera (IFOSC), the main back-end instrument on the IUCAA 2-m telescope at Girawali, Pune, India. This IFU enables IFOSC to perform two-dimensional spectroscopy of extended astronomical objects and is being used as one of the modes of IFOSC. Based on the concept of coupling the telescope focal plane with the spectrograph slit using a fibre bundle, the IFU (named the Fibre-based Integral Field Unit for IFOSC, hereafter FIFUI) uses 100 optical fibres, each associated with a tiny lenslet on its tip, to sample the incoming field of view spatially. In addition, FIFUI uses some coupling optics to realize this two-dimensional interface. FIFUI offers three different spatial sampling scales of 0.8, 1.0 and 1.2 arcsec fibre−1. It is optimized for the visible spectrum and for a field of view of ∼13 × 6 arcsec2 on the sky for the nominal 1-arcsec sampling mode. FIFUI was commissioned on the IUCAA 2-m telescope during 2010 February–March after a series of sky tests and science-verification observations and a dataanalysis pipeline was developed to extract the spectra and reconstruct the sky maps. Here we report on the development of FIFUI, including its opto-mechanical design and commissioning observations.
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    SN 2008gz − most likely a normal type IIP event
    (Mon. Not. R. Astron. Soc., 2011-02-08) Roy, Rupak; Kumar, Brijesh; Moskvitin, Alexander S; et.al
    We present BV RI photometric and low-resolution spectroscopic investigation of a type II core-collapse supernova (SN) 2008gz, which occurred in a star forming arm and within a half-light radius (solar metallicity region) of a nearby spiral galaxy NGC 3672. The SN event was detected late, and a detailed investigation of its light curves and spectra spanning 200 days suggest that it is an event of type IIP similar to archetypal SNe 2004et and 1999em. However, in contrast to other events of its class, the SN 2008gz exhibits rarely observed V magnitude drop of 1.5 over the period of a month during plateau to nebular phase. Using 0.21 mag of AV as a lower limit and a distance of 25.5 Mpc, we estimate synthesized 56Ni mass of 0.05 ± 0.01M⊙ and a mid-plateau MV of −16.6 ± 0.2 mag. The photospheric velocity is observed to be higher than that was observed for SN 2004et at similar epochs, indicating explosion energy was comparable to or higher than SN 2004et. Similar trend was also seen for the expansion velocity of H-envelopes. By comparing its properties with other well studied events as well as by using a recent simulation of pre-SN models of Dessart, Livne & Waldman (2010), we infer an explosion energy range of 2−3×1051 erg and this coupled with the observed width of the forbidden [O i] 6300-6364°A line at 275 days after the explosion gives an upper limit for the main-sequence (non-rotating, solar metallicity) progenitor mass of 17M⊙. Our narrow-band Hα observation, taken nearly 560 days after the explosion and the presence of an emission kink at zero velocity in the Doppler corrected spectra of SN indicate that the event took place in a low luminosity star forming Hii region.
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    SN 2008in − BRIDGING THE GAP BETWEEN NORMAL AND FAINT SUPERNOVAE OF TYPE IIP
    (2011-06-10) Roy, Rupak; Kumar, Brijesh Kumar; Benetti, Stefano; et.al
    We present optical photometric and low-resolution spectroscopic observations of the Type II plateau supernova (SN) 2008in, which occurred in the outskirts of the nearly face-on spiral galaxy M 61. Photometric data in the X-rays, ultraviolet and near-infrared bands have been used to characterize this event. The SN field was imaged with the ROTSE-IIIb optical telescope about seven days before the explosion. This allowed us to constrain the epoch of the shock breakout to JD = 2454825.6. The duration of the plateau phase, as derived from the photometric monitoring, was 98 days. The spectra of SN 2008in show a striking resemblance to those of the archetypal low-luminosity IIP SNe 1997D and 1999br. A comparison of ejecta kinematics of SN 2008in with the hydrodynamical simulations of Type IIP SNe by Dessart et al. (2010) indicates that it is a less energetic event ( 5 × 1050 erg). However, the light curve indicates that the production of radioactive 56Ni is significantly higher than that in the low-luminosity SNe. Adopting an interstellar absorption along the SN direction of AV 0.3 mag and a distance of 13.2 Mpc, we estimated a synthesized 56Ni mass of 0.015M⊙. Employing semi-analytical formulae (Litvinova & Nadezhin 1985), we derived a pre-SN radius of 126R⊙ , an explosion energy of 5.4 × 1050 erg and a total ejected mass of 16.7M⊙ . The latter indicates that the zero age main-sequence mass of the progenitor did not exceed 20M⊙ . Considering the above properties of SN 2008in and its occurrence in a region of sub-solar metallicity ([O/H] 8.44 dex), it is unlikely that fall-back of the ejecta onto a newly formed black hole occurred in SN 2008in. We therefore favor a low-energy explosion scenario of a relatively compact, moderate-mass progenitor star that generates a neutron star.
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    Star Formation Activity in the Galactic H ii Complex S255-S257
    (2011-06-09) Ojha, D.K.; Samal, M.R; Pandey, A.K.; et.al
    We present results on the star-formation activity of an optically obscured region containing an embedded cluster (S255-IR) and molecular gas between two evolved H ii regions S255 and S257. We have studied the complex using optical, near-infrared (NIR) imaging, optical spectroscopy and radio continnum mapping at 15 GHz, along with Spitzer-IRAC results. It is found that the main exciting sources of the evolved H ii regions S255 and S257 and the compact H ii regions associated with S255-IR are of O9.5 - B3 V nature, consistent with previous observations. Our NIR observations reveal 109 likely young stellar object (YSO) candidates in an area of 40.9 40.9 centered on S255-IR, which include 69 new YSO candidates. To see the global star formation, we constructed the V 􀀀I=V diagram for 51 optically identified IRAC YSOs in an area of 130 130 centered on S255-IR. We suggest that these YSOs have an approximate age between 0.1 - 4 Myr, indicating a non-coeval star formation. Using spectral energy distribution (SED) models, we constrained physical properties and evolutionary status of 31 and 16 YSO candidates outside and inside the gas ridge, respectively. The models suggest that the sources associated within the gas ridge are of younger population (mean age 1.2 Myr) than the sources outside the gas ridge (mean age 2.5 Myr). The positions of the young sources inside the gas ridge at the interface of the H ii regions S255 and S257, favor a site of induced star formation
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    THE DISCOVERY AND NATURE OF THE OPTICAL TRANSIENT CSS100217:102913+404220
    (The Astrophysical Journal, 2011-07-10) Drake, A.J; Djorgovski, S.G; Mahabal, A; et.al
    We report on the discovery and observations of the extremely luminous optical transient CSS100217:102913+404220 (CSS100217 hereafter). Spectroscopic observations showed that this transient was coincident with a galaxy at redshift z = 0.147 and reached an apparent magnitude of V ∼ 16.3. After correcting for foreground Galactic extinction we determine the absolute magnitude to be MV = −22.7 approximately 45 days after maximum light. Over a period of 287 rest-frame days, this event had an integrated bolometric luminosity of 1.3 × 1052 erg based on time-averaged bolometric corrections of ∼15 from V- and R-band observations. Analysis of the pre-outburst Sloan Digital Sky Survey (SDSS) spectrum of the source shows features consistent with a narrow-line Seyfert 1 galaxy. High-resolution Hubble Space Telescope and Keck follow-up observations show that the event occurred within 150 pc of the nucleus of the galaxy, suggesting a possible link to the active nuclear region. However, the rapid outburst along with photometric and spectroscopic evolution are much more consistent with a luminous supernova. Line diagnostics suggest that the host galaxy is undergoing significant star formation. We use extensive follow-up of the event along with archival Catalina Sky Survey NEO search and SDSS data to investigate the three most likely sources of such an event: (1) an extremely luminous supernova, (2) the tidal disruption of a star by the massive nuclear black hole, and (3) variability of the central active galactic nucleus (AGN). We find that CSS100217 was likely an extremely luminous Type IIn supernova and occurred within the range of the narrow-line region of an AGN. We discuss how similar events may have been missed in past supernova surveys because of confusion with AGN activity.
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    Photometric study ofWUMa type binaries in the intermediate open cluster NGC 7789
    (Research in Astron. Astrophys., 2010-04-25) Kandulapati, Sriram; Pasagada, Vivekananda Rao
    The light curve solutions of twoWUMa binary systems in the intermediate open cluster NGC 7789 are presented in this paper. These variables were observed using the 2m telescope of the IUCAA-Girawali Observatory. The V passband photometric solutions of the two W UMa binaries were obtained using the latest version of theW–D program. The result shows that both systems are H-subtypeWUMa binaries with high mass ratios.
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    Evidence of V -band polarimetric separation of carbon stars at high Galactic latitude
    (2010-09-20) Goswami, Aruna; Kartha, Sreeja S
    Polarization is an important indicator of stellar evolution, especially for stars evolving from red-giant stage to planetary nebulae. However, not much is known about the polarimetric properties of the carbon-enhanced metal-poor (CEMP) stars, although they have been well studied in terms of photometric as well as lowand high-resolution spectroscopy. We report here rst-ever estimates of V -band polarimetry of a group of CEMP stars. V -band polarimetry was planned as the V -band is known to show maximum polarization among BVRI polarimetry for any scattering of light caused due to dust. Based on these estimates the program stars show a distinct classi cation into two: one with p% < 0.4 and the other with p% > 1. Stars with circumstellar material exhibit a certain amount of polarization that may be caused by scattering of starlight due to circumstellar dust distribution into non-spherically symmetric envelopes. The degree of polarization increases with asymmetries present in the geometry of the circumstellar dust distribution. Our results re ect upon these properties. While the sample size is relatively small, the polarimetric separation of the two groups (p% < 0.4 and p% > 1) is very distinct; this nding, therefore, opens up an avenue of exploration with regard to CEMP stars
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    An ingress and a complete transit of HD80606 b
    (Mon. Not. R. Astron. Soc., 2010-02-04) Hidas, M. G; Tsapras, Y; Mislis, D
    We have used four telescopes at different longitudes to obtain near-continuous light-curve coverage of the star HD80606 as it was transited by its ∼4-MJup planet. The observations were performed during the predicted transit windows around 2008 October 25 and 2009 February 14. Our data set is unique in that it simultaneously constrains the duration of the transit and the planet’s period. Our Markov Chain Monte Carlo analysis of the light curves, combined with constraints from radial-velocity data, yields system parameters consistent with previously reported values. We find a planet-to-star radius ratio marginally smaller than previously reported, corresponding to a planet radius of Rp = 0.921 ± 0.036RJup.
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    A CCD photometric study of the newly discovered contact binary ASAS 134738+0410.1
    (Bull. Astr. Soc. India, 2010-05-21) Deb, Sukanta; Singh, Harinder P.; Seshadri, T. R
    We present a CCD photometric study of the star with ASAS ID 134738+0410.1 using V band observations obtained from the IUCAA Girawali Observatory (IGO) 2-metre telescope, India. The star was selected from the Scuti database of All Sky Automated Survey (ASAS) (Pojmanski 2002). Our analysis reveals that the star is not a Scuti variable but is in fact a W UMa type contact binary with an orbital period of 0.2853067 day. Two new times of primary and secondary minima were determined from the observed data. A preliminary solution obtained using the Wilson-Devinney light curve modelling technique indicates that the star is more likely a partially-eclipsingWUMa type contact binary. However, the determination of actual subtype of this binary is quite impossible from the photometry alone, as the observed light curve can fitted for both A- and W-type solutions. The exact classification of this binary needs to be determined from high resolution spectroscopy.
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    A CCD photometric study of the late type contact binary EK Comae Berenices
    (2010-04-24) Deb, Sukanta; Singh, Harinder P.; Seshadri, T.R
    We present CCD photometric observations of the W UMa type contact binary EK Comae Berenices using the 2 m telescope of IUCAA Girawali Observatory, India. The star was classified as aWUMa type binary of subtype-W by Samec et al. (1996). The new V band photometric observations of the star reveal that shape of the light curve has changed significantly from the one observed by Samec et al. (1996). A detailed analysis of the light curve obtained from the high-precision CCD photometric observations of the star indicates that EK Comae Berenices is not a W-type but an A-type totally eclipsing W UMa contact binary. The photometric mass ratio is determined to be 0.349 ± 0.005. A temperature difference of DT = 141 ± 10 K between the components and an orbital inclination of i[ ] = 89.800 ± 0.075 were obtained for the binary system. Absolute values of masses, radii and luminosities are estimated by means of the standard mass-luminosity relation for zero age main-sequence stars. The star shows O’Connell effect, asymmetries in the light curve shape around the primary and secondary maximum. The observed O’Connell effect is explained by the presence of a hot spot on the primary component.