Shriharsh P. Tendulkar

Publications (8)6.02 Total impact

• Article: Bringing the Visible Universe into Focus with Robo-AO

  Christoph Baranec, Reed Riddle, Nicholas M. Law, A. N. Ramaprakash, Shriharsh P. Tendulkar, Khanh Bui, Mahesh P. Burse, Pravin Chordia, Hillol K. Das, Jack T. C. Davis, Richard G. Dekany, Mansi M. Kasliwal, Shrinivas R. Kulkarni, Timothy D. Morton, Eran O. Ofek, Sujit Punnadi
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  ABSTRACT: Light from astronomical objects must travel through the earth's turbulent atmosphere before it can be imaged by ground-based telescopes. To enable direct imaging at maximum theoretical angular resolution, advanced techniques such as those employed by the Robo-AO adaptive-optics system must be used.
  02/2013;
• Article: The Robo-AO software: Fully autonomous operation of a laser guide star adaptive optics and science system

  Reed L. Riddle, Mahesh P. Burse, Nicholas M. Law, Shriharsh P. Tendulkar, Christoph Baranec, Alexander R. Rudy, Marland Sitt, Ankit Arya, Athanasios Papadopoulos, A. N. Ramaprakash, Richard G. Dekany
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  ABSTRACT: Robo-AO is the first astronomical laser guide star adaptive optics (AO) system designed to operate completely independent of human supervision. A single computer commands the AO system, the laser guide star, visible and near-infrared science cameras (which double as tip-tip sensors), the telescope, and other instrument functions. Autonomous startup and shutdown sequences as well as concatenated visible observations were demonstrated in late 2011. The fully robotic software is currently operating during a month long demonstration of Robo-AO at the Palomar Observatory 60-inch telescope.
  01/2013;
• Article: Bringing the Visible Universe into Focus with Robo-AO.

  Christoph Baranec, Reed Riddle, Nicholas M Law, A N Ramaprakash, Shriharsh P Tendulkar, Khanh Bui, Mahesh P Burse, Pravin Chordia, Hillol K Das, Jack T C Davis, Richard G Dekany, Mansi M Kasliwal, Shrinivas R Kulkarni, Timothy D Morton, Eran O Ofek, Sujit Punnadi
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  ABSTRACT: The angular resolution of ground-based optical telescopes is limited by the degrading effects of the turbulent atmosphere. In the absence of an atmosphere, the angular resolution of a typical telescope is limited only by diffraction, i.e., the wavelength of interest, λ, divided by the size of its primary mirror's aperture, D. For example, the Hubble Space Telescope (HST), with a 2.4-m primary mirror, has an angular resolution at visible wavelengths of ~0.04 arc seconds. The atmosphere is composed of air at slightly different temperatures, and therefore different indices of refraction, constantly mixing. Light waves are bent as they pass through the inhomogeneous atmosphere. When a telescope on the ground focuses these light waves, instantaneous images appear fragmented, changing as a function of time. As a result, long-exposure images acquired using ground-based telescopes - even telescopes with four times the diameter of HST - appear blurry and have an angular resolution of roughly 0.5 to 1.5 arc seconds at best. Astronomical adaptive-optics systems compensate for the effects of atmospheric turbulence. First, the shape of the incoming non-planar wave is determined using measurements of a nearby bright star by a wavefront sensor. Next, an element in the optical system, such as a deformable mirror, is commanded to correct the shape of the incoming light wave. Additional corrections are made at a rate sufficient to keep up with the dynamically changing atmosphere through which the telescope looks, ultimately producing diffraction-limited images. The fidelity of the wavefront sensor measurement is based upon how well the incoming light is spatially and temporally sampled(1). Finer sampling requires brighter reference objects. While the brightest stars can serve as reference objects for imaging targets from several to tens of arc seconds away in the best conditions, most interesting astronomical targets do not have sufficiently bright stars nearby. One solution is to focus a high-power laser beam in the direction of the astronomical target to create an artificial reference of known shape, also known as a 'laser guide star'. The Robo-AO laser adaptive optics system(2,3) employs a 10-W ultraviolet laser focused at a distance of 10 km to generate a laser guide star. Wavefront sensor measurements of the laser guide star drive the adaptive optics correction resulting in diffraction-limited images that have an angular resolution of ~0.1 arc seconds on a 1.5-m telescope.
  Journal of Visualized Experiments 01/2013;
• Article: Proper Motions and Origins of SGR 1806-20 and SGR 1900+14

  Shriharsh P. Tendulkar, P. Brian Cameron, Shrinivas R. Kulkarni
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  ABSTRACT: We present results from high-resolution infrared observations of magnetars SGR1806-20 and SGR 1900+14 over 5 years using laser-supported adaptive optics at the 10-m Keck Observatory. Our measurements of the proper motions of these magnetars provide robust links between magnetars and their progenitors and provide age estimates for magnetars. At the measured distances of their putative associations, we measure the linear transverse velocity of SGR 1806-20 to be 350 +/- 100 km/s and of SGR 1900+14 to be 130 +/- 30 km/s. The transverse velocity vectors for both magnetars point away from the clusters of massive stars, solidifying their proposed associations. Assuming that the magnetars were born in the clusters, we can estimate the braking index to be ~1.8 for SGR 1806-20 and ~1.2 for SGR 1900+14. This is significantly lower than the canonical value of n = 3 predicted by the magnetic dipole spin-down suggesting an alternative source of dissipation such as twisted magnetospheres or particle winds.
  10/2012;
• Article: Millions of Multiples: Detecting and Characterizing Close-Separation Binary Systems in Synoptic Sky Surveys

  Emil Terziev, Nicholas M. Law, Iair Arcavi, Christoph Baranec, Joshua S. Bloom, Khanh Bui, Mahesh P. Burse, Pravin Chorida, H. K. Das, Richard G. Dekany, Adam L. Kraus, S. R. Kulkarni, Peter Nugent, Eran O. Ofek, Sujit Punnadi, A. N. Ramaprakash, Reed Riddle, Shriharsh P. Tendulkar
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  ABSTRACT: The direct detection of binary systems in wide-field surveys is limited by the size of the stars' point-spread-functions (PSFs). A search for elongated objects can find closer companions, but is limited by the precision to which the PSF shape can be calibrated for individual stars. We have developed the BinaryFinder algorithm to search for close binaries by using precision measurements of PSF ellipticity across wide-field survey images. We show that the algorithm is capable of reliably detecting binary systems down to approximately 1/5 of the seeing limit, and can directly measure the systems' position angles, separations and contrast ratios. To verify the algorithm's performance we evaluated 100,000 objects in Palomar Transient Factory (PTF) wide-field-survey data for signs of binarity, and then used the Robo-AO robotic laser adaptive optics system to verify the parameters of 44 high-confidence targets. We show that BinaryFinder correctly predicts the presence of close companions with a <5% false-positive rate, measures the detected binaries' position angles within 2 degrees and separations within 25%, and weakly constrains their contrast ratios. When applied to the full PTF dataset, we estimate that BinaryFinder will discover and characterize ~450,000 physically-associated binary systems with separations <2 arcseconds and magnitudes brighter than R=18. New wide-field synoptic surveys with high sensitivity and sub-arcsecond angular resolution, such as LSST, will allow BinaryFinder to reliably detect millions of very faint binary systems with separations as small as 0.1 arcseconds.
  10/2012;
• Article: PTF 10fqs: A Luminous Red Nova in the Spiral Galaxy Messier 99

  Mansi M. Kasliwal, Shri R. Kulkarni, Iair Arcavi, Robert M. Quimby, Eran O. Ofek, Peter Nugent, Janet Jacobsen, Avishay Gal-Yam, Yoav Green, Ofer Yaron, [......], Gustavo Rahmer, David Hale, Roger Smith, Jeff Zolkower, Viswa Velur, Richard Walters, John Henning, Kahnh Bui, Dan McKenna, and Cullen Blake
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  ABSTRACT: The Palomar Transient Factory (PTF) is systematically charting the optical transient and variable sky. A primary science driver of PTF is building a complete inventory of transients in the local universe (distance less than 200 Mpc). Here, we report the discovery of PTF 10fqs, a transient in the luminosity "gap" between novae and supernovae. Located on a spiral arm of Messier 99, PTF 10fqs has a peak luminosity of Mr = –12.3, red color (g – r = 1.0), and is slowly evolving (decayed by 1 mag in 68 days). It has a spectrum dominated by intermediate-width Hα (930 km s–1) and narrow calcium emission lines. The explosion signature (the light curve and spectra) is overall similar to that of M85 OT2006-1, SN 2008S, and NGC 300 OT. The origin of these events is shrouded in mystery and controversy (and in some cases, in dust). PTF 10fqs shows some evidence of a broad feature (around 8600 Å) that may suggest very large velocities (10,000 km s–1) in this explosion. Ongoing surveys can be expected to find a few such events per year. Sensitive spectroscopy, infrared monitoring, and statistics (e.g., disk versus bulge) will eventually make it possible for astronomers to unravel the nature of these mysterious explosions.
  The Astrophysical Journal 03/2011; 730(2):134. · 6.02 Impact Factor
• Source

  Available from: ArXiv

  Article: PTF10iya: A short-lived, luminous flare from the nuclear region of a star-forming galaxy

  S. Bradley Cenko, Joshua S. Bloom, S. R. Kulkarni, Linda E. Strubbe, Adam A. Miller, Nathaniel R. Butler, Robert M. Quimby, Avishay Gal-Yam, Eran O. Ofek, Eliot Quataert, [......], Isobel M. Hook, D. Andrew Howell, David J. Lagattuta, Nicholas M. Law, Mansi M. Kasliwal, Peter E. Nugent, Jeffrey M. Silverman, Mark Sullivan, Shriharsh P. Tendulkar, Ofer Yaron
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  ABSTRACT: We present the discovery and characterisation of PTF10iya, a short-lived (dt ~ 10 d, with an optical decay rate of ~ 0.3 mag per d), luminous (M_g ~ -21 mag) transient source found by the Palomar Transient Factory. The ultraviolet/optical spectral energy distribution is reasonably well fit by a blackbody with T ~ 1-2 x 10^4 K and peak bolometric luminosity L_BB ~ 1-5 x 10^44 erg per s (depending on the details of the extinction correction). A comparable amount of energy is radiated in the X-ray band that appears to result from a distinct physical process. The location of PTF10iya is consistent with the nucleus of a star-forming galaxy (z = 0.22405 +/- 0.00006) to within 350 mas (99.7 per cent confidence radius), or a projected distance of less than 1.2 kpc. At first glance, these properties appear reminiscent of the characteristic "big blue bump" seen in the near-ultraviolet spectra of many active galactic nuclei (AGNs). However, emission-line diagnostics of the host galaxy, along with a historical light curve extending back to 2007, show no evidence for AGN-like activity. We therefore consider whether the tidal disruption of a star by an otherwise quiescent supermassive black hole may account for our observations. Though with limited temporal information, PTF10iya appears broadly consistent with the predictions for the early "super-Eddington" phase of a solar-type star disrupted by a ~ 10^7 M_sun black hole. Regardless of the precise physical origin of the accreting material, the large luminosity and short duration suggest that otherwise quiescent galaxies can transition extremely rapidly to radiate near the Eddington limit; many such outbursts may have been missed by previous surveys lacking sufficient cadence.
  03/2011;
• Source

  Available from: Derek B. Fox

  Article: PTF10fqs: A Luminous Red Nova in the Spiral Galaxy Messier 99

  Mansi M. Kasliwal, S. R. Kulkarni, Iair Arcavi, Robert M. Quimby, Eran O. Ofek, Peter Nugent, Janet Jacobsen, Avishay Gal-Yam, Yoav Green, Ofer Yaron, [......], Gustavo Rahmer, David Hale, Roger Smith, Jeff Zolkower, Viswa Velur, Richard Walters, John Henning, Kahnh Bui, Dan McKenna, Cullen Blake
  [show abstract] [hide abstract]
  ABSTRACT: The Palomar Transient Factory (PTF) is systematically charting the optical transient and variable sky. A primary science driver of PTF is building a complete inventory of transients in the local Universe (distance less than 200 Mpc). Here, we report the discovery of PTF10fqs, a transient in the luminosity "gap" between novae and supernovae. Located on a spiral arm of Messier 99, PTF 10fqs has a peak luminosity of Mr = -12.3, red color (g-r = 1.0) and is slowly evolving (decayed by 1 mag in 68 days). It has a spectrum dominated by intermediate-width H (930 km/s) and narrow calcium emission lines. The explosion signature (the light curve and spectra) is overall similar to thatof M85OT2006-1, SN2008S, and NGC300OT. The origin of these events is shrouded in mystery and controversy (and in some cases, in dust). PTF10fqs shows some evidence of a broad feature (around 8600A) that may suggest very large velocities (10,000 km/s) in this explosion. Ongoing surveys can be expected to find a few such events per year. Sensitive spectroscopy, infrared monitoring and statistics (e.g. disk versus bulge) will eventually make it possible for astronomers to unravel the nature of these mysterious explosions.
  05/2010;