IGO Publications

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Optical Spectroscopy of Candidates of Young Stellar Objects in NGC 1333
(2001-01-01) Itoh, Yoichi; Gupta, Ranjan; Oasa, Yumiko
We carried out low-resolution optical spectroscopy of 14 low-luminosity young stellar object (YSO) candidates in the NGC 1333 cluster. These objects were previously identified by the near-infrared imaging survey. Eleven objects were confirmed as YSOs by the H line emission. Strengths of the H emission are correlated with the near-infrared excesses of the objects. Spectral types of all YSOs are estimated to be M-type, indicative of low-mass. Comparisons of the results of our spectroscopic observations and the previous photometric observations with evolutionary tracks on the HR diagram suggest two objects to be young brown dwarfs.
IUCAA 2 meter telescope and its first light instrument IFOSC
(Bull. Astr. Soc. India, 2002-06-05) Gupta, Ranjan; Burse, Mahesh P.; Das, H.K.; Kohok, A.; Ramaprakash, A.N; Engineer, S.; Tandon, S. N.
The various features of the IUCAA 2-meter telescope, its site parameters and considerations made for preserving the local seeing in terms of ventilation, thermal emissivity of the dome etc are described. The first light back-end instrument for this telescope, i.e. Iucaa Faint Object Spectrometer and Camera (IFOSC), too is described in some detai
A giant radio jet ejected by an ultramassive black hole in a single-lobed radio galaxy
(2004-12-04) Bagchi, Joydeep; Krishna, Gopal; Krause, Marita; Santosh Joshi
We report the discovery of a very unusual, highly asymmetric radio galaxy whose radio jet, the largest yet detected, emits strongly polarized synchrotron radiation and can be traced all the way from the galactic nucleus to the hot spot located 440 kpc away. This jet emanates from an extremely massive black-hole (> 109M⊙) and forms a strikingly compact radio lobe. No radio lobe is detected on the side of the counter-jet, even though it is similar to the main jet in brightness up to a scale of tens of kilo parsecs. Thus, contrary to the nearly universal trend, the brightness asymmetry in this radio galaxy increases with distance from the nucleus. With several unusual properties, including a predominantly toroidal magnetic field, this Fanaroff-Riley type II mega-jet is an exceptionally useful laboratory for testing the role of magnetic field in jet stabilization and radio lobe formation
Exposure time calculator for IFOSC and sky background estimation
(Bull. Astr. Soc. India, 2005-06-22) Chakraborty, Pavan; Das, H.K.; Tandon, S. N.
This paper describes a spectroscopy exposure time calculator for the faint object spectrograph, the \IUCAA Faint Object Spectrograph" (IFOSC). It is intended to provide reasonable estimates of exposure times for observations. The background sky brightness is modeled for different phases and angular distance from the Moon. The code automatically calculates the Lunar Ephemerides from the date and time of observations and uses it for sky brightness computations. We adopt a new technique of scaling the Rayleigh and the Mie scattering functions, according to the corresponding extinction terms. This estimation of the sky brightness with moonlight ¯ts reasonably well with the observed sky brightness measured at the IUCAA telescope site. A simple component model is used for the optical elements. Each compo- nent is described by simple wavelength dependent extinction tables. At present, a blackbody/power-law spectrum is chosen as the input spectrum. Model or actual spectrum can also be used. The input blackbody spectrum is computed using the stellar \Spectral type" and scaled by the apparent V magnitude of the star. The programme is easily con¯gurable for di®erent sites and instruments. The code is written in ANSI C and thus portable to any system. A graphically interactive interface using HTML-cgi script has also been developed.
Analysis of possible anomalies in the QSO distribution of the Flesch & Hardcastle catalogue
(2008-01-02) M. L´opez-Corredoira; C. M. Guti´errez; Mohan, V.; Gunthardt, G. I.; Alonso, M. S.
Aims. A recent catalogue by Flesch & Hardcastle presents two major anomalies in the spatial distribution of QSO candidates: i/ an apparent excess of such objects near bright galaxies, and ii/ an excess of very bright QSO candidates compared to random background expectations in several regions of the sky. Because anyone of these anomalies would be relevant in a cosmological context, we carried out an extensive analysis of the probabilities quoted in that catalogue. Methods. We determine the nature and redshift of a subsample of 30 sources in that catalogue by analysing their optical spectra (another 11 candidates were identified from existing public databases). These have allowed us to statistically check the reliability of the probabilities QSO status quoted by Flesch & Hardcastle for their candidates. Results. Only 12 of the 41 candidates turned out QSOs (7 of which have been identified here for the first time). Conclusions. The probabilities of the QSOs’ being the candidates given by Flesch & Hardcastle are overestimated for mB ≤ 17 and for objects projected near (≤ 1 arcmin) bright galaxies. This is the cause of the anomalies mentioned above.
Multi-wavelength observations of afterglow of GRB080319B and the modeling constraints
(2009-04-11) Pandey, S.B.; Castro-Tirado, A. J.; Jelinek, M.; et al.
Context. We present observations of the afterglow of GRB 080319B at optical, mm and radio frequencies from a few hours to 67 days after the burst. Aims. To understand the nature of this brightest explosion based on the observed properties and it’s comparison with the afterglow models. Methods. Present observations along with other published multi-wavelength data have been used to study the light-curves and spectral energy distributions of the burst afterglow. Results. Our results show that the observed features of the afterglow fits equally good with the Inter Stellar Matter and the Stellar Wind density profiles of the circum-burst medium. In case of both density profiles, location of the maximum synchrotron frequency νm is below optical and the value of cooling break frequency νc is below X−rays, ∼ 104 s after the burst. Also, the derived value of the Lorentz factor at the time of naked eye brightness is ∼ 300 with the corresponding blast wave size of ∼ 1018 cm. Conclusions. The numerical
Photometric Study ofWUMa Type Binaries in the Old Open Cluster Berkeley 39
(2009-07-06) Sriram, K; Y, Ravi Kiron; P, Vivekananda Rao
The study of W UMa binary systems give a wealth of information about its nature as well as about its parent body (if any), like clusters. In this paper, we present the I passband photometric solutions of fourWUMa binaries in the open cluster Berkeley 39 using the latest version of W–D program. The result shows that, two binary systems are W-subtype W UMa binary systems and another two systems are H-subtype W UMa binary systems. No third body is found in any of the four systems. We found a correlation between the period and mass-ratio as well as temperature and mass-ratio for the respective variables which is similar to the relationship between mass ratio and total mass of the contact binaries as shown by van’t Veer (1996) and Li et al. (2008).
A diffuse bubble-like radio-halo source MRC 0116+111: imprint of AGN feedback in a low-mass cluster of galaxies
(2009-07-09) Bagchi, Joydeep; Jacob, Joe; Gopal, Krishna; et al.
We present detailed observations of MRC 0116+111, revealing a luminous, mini radiohalo of 240 kpc diameter located at the centre of a cluster of galaxies at redshift z = 0.131. Our optical and multi-wavelength GMRT and VLA radio observations reveal a highly unusual radio source: showing a pair of giant ( 100 kpc diameter) bubble-like diffuse structures, that are about three times larger than the analogous extended radio emission observed in M87 - the dominant central radio galaxy in the Virgo Cluster. However, in MRC 0116+111 we do not detect any ongoing Active Galactic Nucleus (AGN) activity, such as a compact core or active radio jets feeding the plasma bubbles. The radio emitting relativistic particles and magnetic fields were probably seeded in the past by a pair of radio-jets originating in the AGN of the central cD galaxy. The extremely steep high-frequency radio spectrum of the north-western bubble, located 100 kpc from cluster centre, indicates radiation losses, possibly because having detached, it is rising buoyantly and moving away into the putative hot intra-cluster medium. The other bubble, closer to the cluster centre, shows signs of ongoing particle re-acceleration.We estimate that the radio jets which inflated these two bubbles might have also fed enough energy into the intra-cluster medium to create an enormous system of cavities and shock fronts, and to drive a massive outflow from the AGN, which could counter-balance and even quench a cooling flow. Therefore, this source presents an excellent opportunity to understand the energetics and the dynamical evolution of radio-jet inflated plasma bubbles in the hot cluster atmosphere.
SDSS J092712.64+294344.0: recoiling black hole or merging galaxies?
(2009-08-31) Vivek, M; Srianand, R.; Noterdaeme, P; et al.
We report long-slit spectroscopic observations of SDSS J092712+294344 carried-out at the recently commissioned 2m telescope in IUCAA Girawali Observatory, India. This AGN-like source is known to feature three sets of emission lines at zem = 0.6972, 0.7020 and 0.7128. Different scenarios such as a recoiling black hole after asymmetric emission of gravitational waves, binary black holes and possible merging systems are proposed for this object. We test these scenarios by comparing our spectra with that fromthe Sloan Digital Sky Survey (SDSS), obtained 4 years prior to our observations. Comparing the redshifts of [Oiii]λλ4960,5008 we put a 3σ limit on the relative acceleration to be less than 32 km s−1 yr−1 between different emitting regions. Using the 2D spectra obtained at different position angles we show that the [Oiii]λ5008 line from the zem = 0.7128 component is extended beyond the spectral point spread function.We infer the linear extent of this line emitting region is ∼ 8 kpc.We also find a tentative evidence for an offset between the centroid of the [Oiii]λ5008 line at zem = 0.7128 and the QSO trace when the slit is aligned at a position angle of 299◦. This corresponds to the zem = 0.7128 system being at an impact parameter of ∼1 kpc with respect to the zem = 0.6972 in the north west direction. Based on our observations we conclude that the binary black hole model is most unlikely. The spatial extent and the sizes are consistent with both black hole recoil and merging scenarios.
Optical variability of radio-intermediate quasars
(2009-10-08) Goyal, Arti; Krishna, Gopal; Joshi, S; et
We report the results of our intensive intranight optical monitoring of 8 opti- cally bright ‘radio-intermediate quasars’ (RIQs) having flat or inverted radio spectra. The monitoring was carried out in R-band on 25 nights during 2005- 09. On each night only one RIQ was monitored for a minimum duration of ∼ 4 hours (the average being 5.2 hours per night). Using the CCD as an N-star photometer, an intranight optical variability (INOV) detection threshold of ∼ 1–2% was achieved for the densely sampled differential light curves (DLCs) de- rived from our data. These observations amount to a large increase over those reported hitherto for this rare and sparsely studied class of quasars which can, however, play an important role in understanding the link between the dominant varieties of powerful AGN, namely the radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and blazars. Despite the probable presence of rela- tivistically boosted nuclear jets, inferred from their flat/inverted radio spectra, clear evidence for INOV in our extensive observations was detected only on one night. Also, flux variation between two consecutive nights was clearly seen for one of the RIQs. These results demonstrate that as a class, RIQs are much less extreme in nuclear activity compared to blazars. The availability in the literature of INOV data for another 2 RIQs conforming to our selection crite- ria allowed us to enlarge the sample to 10 RIQs (monitored on a total of 42 nights for a minimum duration of ∼ 4 hours per night). The absence of large 2 Goyal et al. amplitude INOV (ψ > 3%) persists in this enlarged sample. This extensive database has enabled us to arrive at the first estimate for the INOV Duty Cy- cle (DC) of RIQs. The DC is found to be small (∼ 9%), increasing to ∼ 14% if the two cases of ‘probable’ INOV are included. The corresponding value is known to be ∼ 60% for BL Lacs and ≈ 15% for both RLQs and RQQs, if they too are monitored for & 4 − 6 hours in each session. Our observations also provide information about the long-term optical variability (LTOV) of RIQs, which is found to be fairly common and reaches typical amplitudes of ≈ 0.1- mag. The light curves of these RIQs are briefly discussed in the context of a theoretical framework proposed earlier for linking this rare kind of quasars to the much better studied dominant classes of quasars.
TELICS—A Telescope Instrument Control System for Small/Medium Sized Astronomical Observatories
(2009-10-12) SRIVASTAVA, MUDIT K.; RAMAPRAKASH, A. N.; Burse, Mahesh P.; et.al
For any modern astronomical observatory, it is essential to have an efficient interface between the telescope and its back-end instruments. However, for small and medium-sized observatories, this requirement is often limited by tight financial constraints. Therefore a simple yet versatile and low-cost control system is required for such observatories to minimize cost and effort. Here we report the development of a modern, multipurpose instrument control system TELICS (Telescope Instrument Control System) to integrate the controls of various instruments and devices mounted on the telescope. TELICS consists of an embedded hardware unit known as a common control unit (CCU) in combination with Linux-based data acquisition and user interface. The hardware of the CCU is built around the ATmega 128 microcontroller (Atmel Corp.) and is designed with a backplane, master-slave architecture. A Qt-based graphical user interface (GUI) has been developed and the back-end application software is based on C/C++. TELICS provides feedback mechanisms that give the operator good visibility and a quick-look display of the status and modes of instruments as well as data. TELICS has been used for regular science observations since 2008 March on the 2 m, f/10 IUCAA Telescope located at Girawali in Pune, India.
Quasars probing intermediate-redshift star-forming galaxies
(2010-01-03) P, Noterdaeme; R, Srianand; V, Mohan
We present a sample of 46 [OIII]-emitting galaxies at z < 0.8 detected in the fibre spectra of quasars from the Sloan Digital Sky Survey, Data Release 7 (SDSS-DR7) through an automatic search procedure. We also detect [O II] and Hβ emission lines from most of these galaxies in the SDSS spectra. We study both the emission and absorption properties of a subsample of 17 galaxies in the redshift range z = 0.4–0.7, where Mg II lines are covered by the SDSS spectra. The measured lower limits on the star formation rates of these galaxies are in the range 0.2–20M yr−1. The emission-line luminosities and (O/H) metallicities from R23 measured in this sample are similar to what is found in normal galaxies at these redshifts. Thus, this constitutes a unique sample of intermediate-redshift star-forming galaxies where we can study the quasi-stellar object (QSO) absorber–galaxy connection. Strong MgII (Wλ2796 1Å) as well as MgI absorption lines are detected in the QSO spectra at the redshift of most of these galaxies. Strong Fe II (Wλ2600 > 1 Å) absorption lines are also generally detected whenever the appropriate wavelength ranges are covered. This suggests that most of these systems could be bona fide damped Lyman α systems. We investigate various possible relations between the MgII rest equivalent widths and the emission-line properties. We find a possible (2σ) correlation between the emission-line metallicity of the galaxies and the MgII rest equivalent width of the absorbers [log(O/H)+12=0.1Wλ2796 +8.27], which could be a consequence of an underlyingmass–metallicity relation. However, [O III]-selected MgII systems represent only aminor fraction of the strong MgII absorbers.We find this cannot be attributed to biases related either to the spectral signal-to-noise ratio or to the brightness of the QSOs. We measure the average observed fluxes (collected into the SDSS fibre) of the [OII] and [O III] lines associated to MgII-selected systems through stacking technique.We find that the average luminosities of emission lines are higher for systems with larger Wλ2796. The stacked luminosities are found to be below the typical detection limit in individual spectra, indicating that faint galaxies can contribute appreciably to the observed population of strong MgII absorbers at intermediate redshifts. We also present long-slit spectroscopic observations of SDSS J113108+202151, the most luminous line-emitting galaxy in our z ≥ 0.4 sample. Surprisingly, we find that the line-emitting region does not coincide with the
Interstellar extinction and polarization – a spheroidal dust grain approach perspective
(2010-01-15) Das, H.K.; Voshchinnikov, N.V.; Il’in, V. B.
We extend and investigate the spheroidal model of interstellar dust grains used to simultaneously interpret the observed interstellar extinction and polarization curves. We compare our model with similar models recently suggested by other authors, study its properties and apply it to fit the normalized extinction A(λ)/AV and the polarizing efficiency P(λ)/A(λ) measured in the near-infrared to far-ultraviolet region for several stars seen through one large cloud. We conclude that the model parameter being the angle between the line of sight and the magnetic field direction can be more or less reliably determined from comparison of the theory and observations. This opens a way to study the spatial structure of interstellar magnetic fields by using multiwavelength photometric and polarimetric observations.
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.
Polarimetric observations of comet 67P/Churyumov-Gerasimenko during its 2008-2009 apparition
(2010-04-01) Hadamcik, E; Sen, A.K.; Levasseur-Regourd, A.C
Context. Remote observations of the light scattered by comet 67P/Churyumov-Gerasimenko dust coma are of major importance to determine the physical properties of the particles and prepare the rendezvous with the ESA/Rosetta spacecraft in 2014. Aims. Light scattering and especially linear polarization observations allow a comparison between di erent coma regions and di erent comets, including comets that have been studied by space probes. Our aim is to retrieve physical properties of the dust particles and to characterize their evolution around perihelion passage. Methods. Recent imaging polarimetric observations have been conducted at Haute-Provence observatory (France) on 2009 March 17-19 at 350 phase angle and at IUCAA Girawali observatory (India) on 2008 December 25-27 at 360 phase angle and on 2009 April 30-May 1 at 290 phase angle. With the imaging technique, the intensity and linear polarization variations are studied through the various coma regions. These observations are compared to other cometary data (e.g. Jupiter family comets) and to numerical and experimental simulations. Results. The decrease in intensity as a function of the distance to nucleus in log-log scale is on average close to -1, although important variations with values down to -1.5 are noticed, in agreement with previous observations in 1982-83 and 1995-96. The intensity along the tailward direction decreases with a slope between -1.2 two months before perihelion (2009 February 28) to -1.0 two months after perihelion; the decrease is more pronounced in the sunward direction. Before perihelion, aperture polarization values are comparable to polarization values measured on other comets at similar phase angles. The sharp decrease in intensity and the feature in the tailward direction, without any di erence in polarization in the coma before perihelion, could suggest the presence of large dark particles. The post-perihelion increase in intensity and in polarization suggests that an outburst has occurred. The freshly ejected dust polarizes more the scattered light and is more sensitive to the solar radiation pressure, suggesting small micron- or submicron-sized grains.
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.
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.
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.
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
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.