Margarita Safonova | Indian Institute of Astrophysics (original) (raw)

Papers by Margarita Safonova

Study of exoplanets is one of the main goals of present research in planetary sciences and astrob... more Study of exoplanets is one of the main goals of present research in planetary sciences and astrobiology. Analysis of huge planetary data from space missions such as CoRoT and Kepler is directed ultimately at finding a planet similar to Earth—the Earth's twin, and answering the question of potential exo-habitability. The Earth Similarity Index (ESI) is a first step in this quest, ranging from 1 (Earth) to 0 (totally dissimilar to Earth). It was defined for the four physical parameters of a planet: radius, density, escape velocity and surface temperature. The ESI is further subdivided into interior ESI (geometrical mean of radius and density) and surface ESI (geometrical mean of escape velocity and surface temperature). The challenge here is to determine which exoplanet parameter(s) is important in finding this similarity ; how exactly the individual parameters entering the interior ESI and surface ESI are contributing to the global ESI. Since the surface temperature entering surface ESI is a non-observable quantity, it is difficult to determine its value. Using the known data for the Solar System objects, we established the calibration relation between surface and equilibrium temperatures to devise an effective way to estimate the value of the surface temperature of exoplanets. ESI is a first step in determining potential exo-habitability that may not be very similar to a terrestrial life. A new approach , called Mars Similarity Index (MSI), is introduced to identify planets that may be habitable to the extreme forms of life. MSI is defined in the range between 1 (present Mars) and 0 (dissimilar to present Mars) and uses the same physical parameters as ESI. We are interested in Mars-like planets to search for planets that may host the extreme life forms, such as the ones living in extreme environments on Earth; for example, methane on Mars may be a product of the methane-specific extremophile life form metabolism.

We provide an in depth study of the theoretical peculiarities that arise in effective negative ma... more We provide an in depth study of the theoretical peculiarities that arise in effective negative mass lensing,
both for the case of a point mass lens and source, and for extended source situations. We describe novel
observational signatures arising in the case of a source lensed by a negative mass. We show that a negative
mass lens produces total or partial eclipse of the source in the umbra region and also show that the usual
Shapiro time delay is replaced with an equivalent time gain. We describe these features both theoretically, as
well as through numerical simulations. We provide negative mass microlensing simulations for various intensity
profiles and discuss the differences between them. The light curves for microlensing events are presented
and contrasted with those due to lensing produced by normal matter. The presence or absence of these features
in the observed microlensing events can shed light on the existence of natural wormholes in the Universe.

We present a set of simulations of the macrolensing e ects produced by large-scale cosmological ... more We present a set of simulations of the macrolensing e ects produced by large-scale cosmological
violations of the energy conditions. These simulations show how the appearance
of a background eld of galaxies is a ected when lensed by a region with an energy
density equivalent to a negative mass ranging from 1012 to 1017 jM j. We compare with
the macrolensing results of equal amounts of positive mass, and show that, contrary
to the usual case where tangential arc-like structures are expected, there appear radial
arcs | runaway laments | and a central void. These results make the cosmological
macrolensing produced by space{time domains where the weak energy conditions are
violated, observationally distinguishable from standard regions. Whether large domains
with negative energy density indeed exist in the universe can now be decided by future
observations of deep fi elds.

The influence of gravitational waves (GW) from binaries in globular clusters on the timing of pul... more The influence of gravitational waves (GW) from binaries in globular clusters on the timing of pulsars situated in this cluster is considered. The probability of observation this effect is estimated. We show that the probability is high enough in clusters Ter 5, M 15, 47 Tuc, NGC 6440. The total list of clusters with pulsars versus probability of event is presented. Total probability of this event reaches 0.97 at least in one cluster.

Astrophysics and Space Science, 2010

With every new discovery of an extra-solar planet, the absence of planets in globular clusters (G... more With every new discovery of an extra-solar planet, the absence of planets in globular clusters (GCs) becomes
more and more conspicuous. Null detection of transiting hot Jupiters in globular clusters 47 Tuc,
omega Cen and NGC6397 presents an important puzzle, raising questions about the role played by cluster
metallicity and environment on formation and survival of planetary systems in densely populated stellar clusters.
GCs were postulated to have many free-floating planets, for which the microlensing (ML) is an established
tool for detection. Dense environment, well-constrained distances and kinematics of lenses and sources, and
photometry of thousands of stars simultaneously make GCs the ideal targets to search for the microlensing.
We present first results of a multi-site, 69-nights long campaign to search for ML signatures of
low-mass objects in the globular cluster M4, which was chosen due to its proximity, location and an actual existence
of a planet. M4 was observed in R and I bands by two telescopes, 1-m T40 and 18-inch C18, of WISE Observatory,
Tel Aviv, Israel, from April to July 2011. Observations on 1-m telescope were carried out in service mode, gathering
6 to 18 20-sec exposures a night for a total of 69 nights. C18 observations were done for about 4 hrs a night for 7
nights in May 2011. We employ the semi-automated pipeline to calibrate and reduce the images to the light curves
that our group is developing for this purpose which includes the differential photometry package DIAPL,
written by Wozniak and modified by W. Pych. Several different diagnostics are employed for search of variability/transients.
While no high-significance ML event was found in this observational run, we have detected more than twenty new variables
and variable candidates in M4 field, which we present here.

Gravitation and Cosmology

In non-minimally coupled effective gravity theories one can have non-topological solitonic soluti... more In non-minimally coupled effective gravity theories one can have non-topological solitonic solutions. A typical solution is a spherical region with G eff =0 outside and having the canonical Newtonian value inside. Such a spherical domain (gravity-ball) is characterized by an effective index of refraction which causes bending of light incident on it. The gravity ball thus acts as a spherical lens. We consider the gravity ball to be of a size of a typical cluster of galaxies and show that even empty (without matter) gravity ball can produce arclike images of the background source galaxy. In the case of background random galaxy field the ball produces distortions (‘shear’) of that field. We also obtained constraints on the size of the large gravity ball, which can be inferred from the existing observations of clusters with arcs.

The TAUVEX Observatory is a collaborative project between the Indian Institute of Astrophysics (I... more The TAUVEX Observatory is a collaborative project between the Indian Institute of Astrophysics (IIA) and Tel Aviv University (TAU) to observe the ultraviolet (UV) sky. TAUVEX Observatory consists of a set of three co-aligned telescopes capable of imaging in the 100 to 350 nm range through a set of 5 different filters. The major science objectives of TAUVEX are (a) searches for QSOs and AGNs based on their UV properties, (b) surface photometry of galaxies in the UV, (c) studies of stars and nebulae within the Galaxy, (d) the nature of the UV background, and (d) studies of variable sources in the UV domain. Science planning for TAUVEX is being conducted by the personnel of the TAUVEX Core Group (TCG). All science operations activities will be based at TAUVEX Data Centre, IIA, Bangalore, India. The Principal Investigators and TAUVEX Science Team have created a coherent observing program to address several key science objectives that will constitute the Core Science Program projects. Th...

Astrophysics and Space Science, 2014

ABSTRACT Space astronomy in the last 40 years has largely been done from spacecraft in low Earth ... more ABSTRACT Space astronomy in the last 40 years has largely been done from spacecraft in low Earth orbit (LEO) for which the technology is proven and delivery mechanisms are readily available. However, new opportunities are arising with the surge in commercial aerospace missions. We describe here one such possibility: deploying a small instrument on the Moon. This can be accomplished by flying onboard the Indian entry to the Google Lunar X PRIZE competition, Team Indus mission, which is expected to deliver a nearly 30 kgs of payloads to the Moon, with a rover as its primary payload. We propose to mount a wide-field far-UV (130–180 nm) imaging telescope as a payload on the Team Indus lander. Our baseline operation is a fixed zenith pointing but with the option of a mechanism to allow observations of different attitudes. Pointing towards intermediate ecliptic latitude (50∘ or above) ensures that the Sun is at least 40∘ off the line of sight at all times. In this position, the telescope can cover higher galactic latitudes as well as parts of Galactic plane. The scientific objectives of such a prospective are delineated and discussed.

The habitable zone (HZ) is defined as the region around a star where a planet can support liquid ... more The habitable zone (HZ) is defined as the region around a star where a planet can support liquid water on its surface, which, together with an oxygen atmosphere, is presumed to be necessary (and sufficient) to develop and sustain life on the planet. Currently, about twenty potentially habitable planets are listed. The most intriguing question driving all these studies is whether planets within habitable zones host extraterrestrial life. It is implicitly assumed that a planet in the habitable zone bears biota. However along with the two usual indicators of habitability, an oxygen atmosphere and liquid water on the surface, an additional one -- the age --- has to be taken into account when the question of the existence of life (or even a simple biota) on a planet is addressed. The importance of planetary age for the existence of life as we know it follows from the fact that the primary process, the photosynthesis, is endothermic with an activation energy higher than temperatures in ha...

Modern Physics Letters A, 2002

A ‘habitable zone’ of a star is defined as a range of orbits within which a rocky planet can supp... more A ‘habitable zone’ of a star is defined as a range of orbits within which a rocky planet can support liquid water on its surface. The most intriguing question driving the search for habitable planets is whether they host life. But is the age of the planet important for its habitability? If we define habitability as the ability of a planet to beget life, then probably it is not. After all, life on Earth has developed within
only ~800 Myr after its formation – the carbon isotope change detected in the oldest rocks indicates the existence of already active life at least 3.8 Gyr ago. If, however, we define habitability as our ability to detect life on the surface of exoplanets, then age becomes a crucial parameter. Only after life had evolved sufficiently complex to change its environment on a planetary scale, can we detect it remotely through its imprint on the atmosphere – the so-called biosignatures, out of which the photosynthetic oxygen is the most prominent indicator of developed (complex) life as we know it. Thus, photosynthesis is a powerful biogenic engine that is known to have changed our planet’s global atmospheric properties. The importance of planetary age for the detectability of life as we know it follows from the fact that this primary process, photosynthesis, is endothermic with an activation energy higher than temperatures in habitable zones, and is sensitive to the particular thermal conditions of the planet. Therefore, the onset of photosynthesis on planets in habitable zones may take much longer time than the planetary age. The knowledge of the age of a planet is necessary for developing a strategy to search for exoplanets carrying complex (developed) life – many confirmed potentially habitable planets are too young (orbiting Population I stars) and may not have had enough time to develop and/or sustain detectable life. In the last decade, many planets orbiting old (9–13 Gyr) metal-poor Population II stars have been discovered. Such planets had had enough time to develop necessary chains of chemical reactions and may carry detectable life if located in a habitable zone. These old planets should be primary targets in search for the extraterrestrial life.

Several planets have recently been discovered around stars that are old and metal-poor, implying ... more Several planets have recently been discovered around stars that are old and metal-poor, implying that these planets are also old, formed in the early Universe together with their hosts. The canonical theory suggests that the conditions for their formation could not have existed at such early epochs. In this paper we argue that the required conditions, such as sufficiently high dust-to-gas ratio, could in fact have existed in the early Universe immediately following the first episode of metal production in Pop. III stars, both in metal-enhanced and metal-deficient environments. Metal-rich regions may have existed in multiple isolated pockets of enriched and weakly-mixed gas close to the massive Pop. III stars. Observations of quasars at redshifts z ∼ 5, and gamma-ray bursts at z ∼ 6, show a very wide spread of metals in absorption from [X/H] −3 to − 0.5. This suggests that physical conditions in the metal-abundant clumps could have been similar to where protoplanets form today. However, planets could have formed even in low-metallicity environments, where formation of stars is expected to proceed due to lower opacity at higher densities. In such cases, the circumstellar accretion disks are expected to rotate faster than their high-metallicity analogues. This in turn can result in the enhancement of dust particles at the disk periphery, where they can coagulate and start forming planetesimals. In conditions with the low initial specific angular momentum of the cloud, radiation from the central protostar can act as a trigger to drive small-scale instabilities with typical masses in the Earth to Jupiter mass range. Discoveries of planets around old metal-poor stars (e.g. HIP 11952, [Fe/H] ∼ −1.95, ∼13 Gyr) show that planets did indeed form in the early Universe and this may require modification of our understanding of the physical processes that produce them. This work is an attempt to provide one such heuristic scenario for the physical basis for their existence.

Modern Physics Letters A, 2003

From the simple Lagrangian the equations of motion for the particle with spin are derived. The sp... more From the simple Lagrangian the equations of motion for the particle with spin are derived. The spin is shown to be conserved on the particle world-line. In the absence of a spin the equation coincides with that of a geodesic. The equations of motion are valid for massless particles as well, since mass does not enter the equations explicitely.

Modern Physics Letters A, 2005

The influence of spin on a photon's motion in a Schwarzschild and FRW spacetimes is studied. The ... more The influence of spin on a photon's motion in a Schwarzschild and FRW spacetimes is studied. The first order correction to the geodesic motion is found. It is shown that unlike the world-lines of spinless particles, the photons world-lines do not lie in a plane.

Astrophysics and Space Science, 2008

Transient events have posed special problems in astronomy because of the intrinsic difficulty of ... more Transient events have posed special problems in astronomy because of the intrinsic difficulty of their detection, and a new class of observatories such as the Pan-STARRS and LSST are coming up specifically to observe these energetic events. In this paper we discuss the UV transient events from two specific sources, such as possible collisions in extrasolar planetary systems and M dwarf flares, to find the probability of their detection by space UV observatories, in particular, by the Tel Aviv University Explorer (TAUVEX). TAUVEX is an UV imaging experiment that will image large parts of the sky in the wavelength region between 1200 and 3500 Å. TAUVEX is a collaborative effort between the Indian Institute of Astrophysics (IIA) and Tel Aviv University, and is scheduled for an early-2009 launch with at least three years of operations. The scientific instrument has been fabricated at El-Op in Israel, with the satellite interfaces, launch and flight operations provided by the Indian Space Research Organization (ISRO). The ground-based software development is the responsibility of the IIA while other aspects of the mission are the joint responsibility of IIA and Tel Aviv University. TAUVEX Science Team (TST) have created a coherent observing program to address several key science objectives, one of them is a program to study short-scale UV transient events. We have estimated that in one year of TAUVEX observations we can expect about 90–350 short-scale transient events. Because we obtain real-time telemetry with TAUVEX, we will be able to catch transients early in their evolution and to alert other observatories. We also present a description of TAUVEX mission, including instrument design and its estimated performance.

The operational tasks for the Performance Veriflcation (PV) and calibration phase in the flrst ye... more The operational tasks for the Performance Veriflcation (PV) and calibration phase in the flrst year of TAUVEX operation are presented. The new challenges regarding the possible reduction in sensitivity are outlined and are re∞ected in the specialized plan for flrst few months of the mission. The calibration operations will be extended into the flrst year, in parallel to an un- precedented deep exposure of the celestial poles. The preliminary zero-points of the instrumental photometric system, in AB and Vega-based magnitude sys- tems, are calculated for pre-ground calibrations data as well as for the updated results. For ∞ux calibration, the efiective wavelengths, bandwidths and con- version factors are calculated for both pre-ground and updated values. These conversion factors are to be used for converting the TAUVEX count rates to ∞ux and UV luminosity of the sources.

Bulletin of The Astronomical Society of India, 2007

Bulletin of The Astronomical Society of India, 2009

The operational tasks for the Performance Verification (PV) and calibration phase in the first ye... more The operational tasks for the Performance Verification (PV) and calibration phase in the first year of TAUVEX operation are presented. The new challenges regarding the possible reduction in sensitivity are outlined and are reflected in the specialized plan for first few months of the mission. The calibration operations will be extended into the first year, in parallel to an unprecedented deep exposure of the celestial poles. The preliminary zero-points of the instrumental photometric system, in AB and Vega-based magnitude systems, are calculated for pre-ground calibrations data as well as for the updated results. For flux calibration, the effective wavelengths, bandwidths and conversion factors are calculated for both pre-ground and updated values. These conversion factors are to be used for converting the TAUVEX count rates to flux and UV luminosity of the sources.