Prof. Dr. Sergio Cellone

   M.Sc. in Astronomy, 1988, UNLP, Argentina, "CCD study of the dwarf galaxy D2 associated with NGC 3115"
Ph.D. in Astronomy, 1994, UNLP, Argentina, "Study of structural properties and stellar populations in low surface brightness galaxies"

Current position: Researcher & Director, Complejo Astronomico El Leoncito (CASLEO), CONICET-UNLP-UNC-UNSJ, Argentina
Professor, Faculty of Astronomical and Geophysical Sciences, University of La Plata (FCAyG-UNLP), Argentina

Publication list
Personal page, outside GARRA


Since 1988 I have been working on topics related to galactic and extragalactic stellar systems, as well as a few breakthroughs in Solar System small bodies. These subjects include:

  • Collaborations with GARRA members:
    1. Optical microvariability of Active Galactic Nuclei (AGNs). Intraday variability of AGNs like quasars and BL Lac objects was discovered 10 years ago during extensive monitoring campaigns of large samples of northern objects. The origin of these variations is still unknown. Shocks propagating down the parsec-scale jet of the objects have been suggested as a possible cause, but the most extreme cases of variability impose severe constraints on the shock thickness and required Doppler factors. Extrinsic models invoke gravitational microlensing. Since 1997 we have made numerous observations of rapid flux variability in southern AGNs, detecting many outstanding outbursts (including the observation of extreme intranight events with amplitudes of up to 1.2 magnitudes in 24 hs). Since 2001, we have also made optical polarimetric observations of blazars, detecting fast polarization variations in some objects.
    2. X-ray binaries (XRBs) are composed by a neutron star or a black hole -the results of a supernova explosion- which orbit a normal star. These sources are powered by the energy released when matter is transferred from the normal star to its compact companion. I have collaborated in the polarimetric study of LS 5039, a high-mass XRB with a microquasar behaviour.
  • Other works
    1. Dwarf galaxies, due to their low masses and sizes, are key objects for the study of star formation in stellar systems. Largely outnumbering their brighter counterparts, dwarfs are also main characters in evolutive scenarios of clusters and groups of galaxies, involving mergers, stripping and interactions. In several works on nearby clusters we have studied the structure and stellar populations in dwarf elliptical galaxies; the results include the first quantification of the luminosity vs. profile shape relation for dwarfs, and the photometric detection of disk-like features in dwarf ellipticals.
    2. Extragalactic globular clusters are excellent test particles to study the kinematics and chemical properties in nearby galaxies out to large galactocentric radii. We have made several observational studies of Galactic globular clusters as well as extragalactic globular clusters systems, involving photometry, polarimetry and medium-resolution spectroscopy, which lead to the detection of dust in Milky Way clusters and the possible identification of free-floating globulars in the Fornax cluster of galaxies.
    3. Asteroids may contain dynamical and chemical information on the origins of our Solar System. Between 1997 and 2001 I was involved in astrometric and photometric studies of asteroids and centaurs.
    4. Between 1996 and 1997 I was Resident Astronomer at the Complejo Astronůmico El Leoncito (CASLEO), the Argentinian astronomical facility which operates a 2.15-m optical telescope. My main duties were: instruments testing (CCD camera, two polarimeters, medium-resolution spectrograph), software developing (under IRAF), creation and maintenance of the web pages, and assitance to observers.