Seminario en Cerro Calan, 23 Mayo 2013, 16:00 hrs.

Only for stars in the Milky Way is it currently possible to examine both the three dimensional kinematics and composition of a central bulge/bar population, offering a unique laboratory for the study of galaxy formation and evolution. I will present the results from the BRAVA spectroscopic survey of giants in the Galactic bulge, and how this database constrains dynamical models of the Galactic bulge and the formation of the Milky Way Galaxy.

Seminario en Cerro Calan, 16 Mayo 2013, 16:00 hrs.

A star orbiting a massive black hole is tidally disrupted when its distance from the hole is smaller than the tidal radius. Many previous studies have focused on studying the tidal disruption of stars in marginally bound orbits using Newtonian mechanics. Tidal disruptions, however, can also happen very close to the event horizon of the hole, where general relativistic effects need to be considered. Also, stars can be captured by massive black holes, inspiral due to gravitational radiation and other effects, and eventually be disrupted in a bound orbit with moderate eccentricity. We show via general relativistic simulations that when a star is disrupted in a close, bound orbit, the temporal behaviors of the stellar debris and tidal flares change qualitatively compared to the standard picture. It is important to study such tidal flares in details, since they are likely to be captured in future time-domain surveys such as using the LSST.

Seminario en Cerro Calan, 25 Abril 2013, 16:00 hrs.

Most of the cross-correlations between temperature anomalies of the Cosmic Microwave Background (CMB) and foreground sources are based on two-dimensional distributions of extragalactic sources. Here we use the third coordinate (redshift) for checking whether some CMB fluctuations might be caused by distant concentrations of matter. We have cross-correlated the redshifts from a sample of 5688 supernovae with WMAP temperatures corresponding to the locations of these sources on the sky and we have found a statistically-significant correlation, with the temperature bias of +0.0299+/-0.0044 mK for the redshifts ranging from 0.5 to 1.0. Such an excess of temperatures is much larger than the current theoretical and observational estimates for potential biases in the CMB temperatures due to extragalactic contamination.

Seminario en Cerro Calan, 22 Abril 2013, 16:00 hrs.

The works of Pulkovo Observatory from its foundation in 1839 to the present day and its actual plans are reviewed.

Seminario en Cerro Calan, 16 Abril 2013, 16:00 hrs.

Massive stars do not explode as they are born. Especially, mass lose during their evolution strongly affects the final fate because of their huge luminosities. However, our knowledge of mass loss is still limited. For example, some supernovae (SNe) show signatures of extensive mass loss which should have happened shortly before their explosions. This kind of mass loss shortly before the explosion is not understood well. I study SNe which show signatures of circumstellar medium (CSM) and investigate mass loss of massive stars shortly before their explosions. I will discuss the CSM signatures of SNe IIb, IIn, and superluminous SNe and the mass loss properties indicated by them. Based on the results, I will discuss the progenitors of SNe showing the effect of CSM and the mass loss mechanisms involved.

Seminario en Cerro Calan, 15 Abril 2013, 16:00 hrs.

The LCDM cosmological model accounts for an impressive array of data on the large-scale structure of the universe, from scales of a few megaparsecs to a few gigaparsecs. On submegaparsec scales, however, the model cannot be tested with the same degree of rigour as on larger scales where microwave background radiation data and measures of galaxy clustering provide clean and well-understood diagnostics. Yet, it is precisely on these small scales that the nature of the dark matter manifests itself most clearly. I will discuss theoretical predictions for the small-scale structure of the universe which appear to be discrepant with recent kinematical data for satellite galaxies of the Milky Way.

Possible solutions range from the relatively mundane - that the mass of our galaxy is smaller than is often thought - through exotic baryonic processes to the more radical assumption that the dark matter is not what the standard theory assumes.

Seminario en Cerro Calan, 11 Abril 2013, 16:00 hrs.

I will present the metallicity and effective temperature techniques developed for M dwarf stars by Rojas-Ayala et al. (2010, 2012). These techniques are based on absorption features present in the modest resolution (R ~2700) K-band spectra of M dwarfs and have been calibrated using FGK+M dwarf pairs and synthetic atmosphere models. I will compare their results with other empirical measurements of low mass stars in the literature, and I will discuss the usefulness of these K-band methods for the characterization of exoplanet systems . Finally, I will show a new technique based on a color-color diagram that can can provide [Fe/H] estimates for M dwarfs in the SDSS and LSST surveys accurate to RMSE = 0.16 dex.

Seminario en Cerro Calan, 04 Abril 2013, 16:00 hrs.

The nearby grand-design spiral galaxy M51 (NGC 5194), which is viewed almost face-on, is ideal for studying molecular gas properties, physical conditions and star formation processes at high spatial resolution with single-dish telescopes. In this paper we present the first complete CO J=3-2 map of M51, at a spatial resolution of 600 pc and covering the entire optical galaxy disk, obtained with the HARP-B instrument on the James Clerk Maxwell Telescope. CO J=3-2 emission is detected over an area of 9' ×6'( 21×14 kpc) and includes emission from across the entire disk of M51 and out to its companion NGC 5195. We describe the CO J=3-2 integrated intensity map and combine our results with maps of CO J=2-1, CO J=1-0 and other data from the literature to investigate the variation of the molecular gas, atomic gas and polycyclic aromatic hydrocarbon (PAH) properties of M51 as a function of distance along the spiral structure on sub-kiloparsec scales. We find that for the CO J=3-2 and CO J=2-1 transitions there is a clear difference between the variation of arm and inter-arm emission with galactocentric radius, with the inter-arm emission relatively constant with radius and the contrast between arm and inter-arm emission decreasing with radius, for CO J=3-2 falling by a factor of 4 from 2 to 6.5 kpc radius. On the other hand, for CO J=1-0 line and Hi emission the variation with radius shows a similar trend for the arm and inter-arm regions, such that the arm–inter-arm contrast appears relatively constant with radius. At a galactocentric radius of 6 kpc, the three CO transitions and the Hi emission all exhibit a similar arm-inter-armcontrast ( 1.5). We have also investigated the variation of CO line ratios (J=3-2/2-1, J=2- 1/1-0 and J=3-2/1-0) as a function of distance along the spiral str?›?????%????????†††††††††††????†††††††††††††††ucture. The CO J=3-2/J=2-1 integrated intensity line ratio varies from 0.1–1.0 over the disk, consistent with the range of typical values for other nearby galaxies in the literature. The highest CO J=3-2/J=2-1 line Aratios are found in the central 1 kiloparsec and in the spiral arms (average values of 0.63 and 0.5, respectively) and the lowest line ratios in the inter-arm regions (average value of 0.4). While we find no clear evidence of a trend with radius for the spiral arms, for the inter-arm regions there appears to be a trend for all the CO line ratios to increase with radius, in the case of CO J=3-2/J=2-1 increasing from 0.3 at 2 kpc to 0.5 at 6 kpc (comparable to the spiral arm value at this radius).
We have investigated the relationship between PAH emission and CO J=3-2 emis- sion and find a strong relationship between the ratio of CO J=3-2 intensity to stellar continuum-subtracted 8µm PAH surface brightness and the CO J=3-2 intensity that appears to vary with radius. The CO J=3-2/PAH 8µm ratio exhibits a decreasing trend with radius. We also find a strong relationship between the CO J=3-2 and 24µm emission.

Seminario en Cerro Calan, 28 Marzo 2013, 16:00 hrs.

The nearby grand-design spiral galaxy M51 (NGC 5194), which is viewed almost face-on, is ideal for studying molecular gas properties, physical conditions and star formation processes at high spatial resolution with single-dish telescopes. In this paper we present the first complete CO J=3-2 map of M51, at a spatial resolution of 600 pc and covering the entire optical galaxy disk, obtained with the HARP-B instrument on the James Clerk Maxwell Telescope. CO J=3-2 emission is detected over an area of 9' ×6'( 21×14 kpc) and includes emission from across the entire disk of M51 and out to its companion NGC 5195. We describe the CO J=3-2 integrated intensity map and combine our results with maps of CO J=2-1, CO J=1-0 and other data from the literature to investigate the variation of the molecular gas, atomic gas and polycyclic aromatic hydrocarbon (PAH) properties of M51 as a function of distance along the spiral structure on sub-kiloparsec scales. We find that for the CO J=3-2 and CO J=2-1 transitions there is a clear difference between the variation of arm and inter-arm emission with galactocentric radius, with the inter-arm emission relatively constant with radius and the contrast between arm and inter-arm emission decreasing with radius, for CO J=3-2 falling by a factor of 4 from 2 to 6.5 kpc radius. On the other hand, for CO J=1-0 line and Hi emission the variation with radius shows a similar trend for the arm and inter-arm regions, such that the arm–inter-arm contrast appears relatively constant with radius. At a galactocentric radius of 6 kpc, the three CO transitions and the Hi emission all exhibit a similar arm-inter-armcontrast ( 1.5). We have also investigated the variation of CO line ratios (J=3-2/2-1, J=2- 1/1-0 and J=3-2/1-0) as a function of distance along the spiral structure. The CO J=3-2/J=2-1 integrated intensity line ratio varies from 0.1–1.0 over the disk, consistent with the range of typical values for other nearby galaxies in the literature. The highest CO J=3-2/J=2-1 line Aratios are found in the central 1 kiloparsec and in the spiral arms (average values of 0.63 and 0.5, respectively) and the lowest line ratios in the inter-arm regions (average value of 0.4). While we find no clear evidence of a trend with radius for the spiral arms, for the inter-arm regions there appears to be a trend for all the CO line ratios to increase with radius, in the case of CO J=3-2/J=2-1 increasing from 0.3 at 2 kpc to 0.5 at 6 kpc (comparable to the spiral arm value at this radius).
We have investigated the relationship between PAH emission and CO J=3-2 emis- sion and find a strong relationship between the ratio of CO J=3-2 intensity to stellar continuum-subtracted 8µm PAH surface brightness and the CO J=3-2 intensity that appears to vary with radius. The CO J=3-2/PAH 8µm ratio exhibits a decreasing trend with radius. We also find a strong relationship between the CO J=3-2 and 24µm emission.

Seminario en Cerro Calan, 21 Marzo 2013, 16:00 hrs.

In this talk, I will present studies of ULIRGs at z~2 with Spitzer, Herschel and Hubble. Dusty galaxies at high redshifts were first observed with submm/mm telescopes. Spectrosocpy for these submm galaxies to identify their redshifts became difficult because of faint optical counterparts. The Spitzer telescope observed large amount of 24micron selected IR galaxies at z~2, and the mid-IR spectroscopy with IRS directly identifies their redshifts. The mid-IR spectroscopy also shows rich spectral features, including PAH emission and slicates absorption features. Recently the Herschel Space Telescope detected those galaxies in FIR bands. The dust temperatures for the MIPS 24 sources are unbiased comparing with submm galaxies biased towards cold dust emission. More recently the HST largest multi cycle program, CANDELS, took deep NIR imaging of 5 fields, permiting studies of the rest-frame optical morphologies of these galaxies.

Seminario en Cerro Calan, 15 Marzo 2013, 12:00-13:00 hrs.

Nature is one of the world's leading scientific journals, publishing many papers that receive wide attention by the general public. But, Nature is very selective of submitted papers are published. In order to maximize your chances of getting published, papers should present fundamental new physical insights, or startling observations/results. Theory papers pose additional problems, as we want only those papers that are likely to be the correct explanation, and not simply exploring parameter space. The writing should be clear, concise and directed at the level of a graduate course in the subject. I encourage authors to contact me in advance of submission of a paper, both to ascertain the appropriateness of the result for Nature, and to ensure that the writing is close to our standards. Posting to ArXiv is and always has been allowed, but authors should discuss the specifics with their institutional public affairs officers before doing so.

Seminario en Cerro Calan, 14 Marzo 2013, 16:00 hrs.

Neutron stars represent many extremes, in density, gravity, and magnetic field strength. Their study therefore probes physics as well as astrophysics frontiers. After giving an overview of neutron stars and their evolution in binaries, I will discuss a number of recent results related to their maximum mass (which holds important clues to the highly uncertain state of matter in their cores) and the difficulties and prospects of measuring their radii. I will conclude by discussing the exciting promise of neutron star measurements using gravitational wave detections.

Seminario en Cerro Calan, 11 Marzo 2013, 16:00 hrs.

I will discuss recent issues in theoretical studies of Type Ia supernova progenitors. (1) For the merging of double C+O white dwarfs (WDs) (DD scenario), one issue is whether the carbon detonation promptly ignites near the surface of the WD. Another issue is, in case of no surface C-detonation, whether the quiescent carbon shell burning ignites to convert the C+O WD into the O+Ne+Mg WD. (2) For the single degenerate (SD) scenario, the issue is whether the missing companions in nearby SNe Ia and SN Ia remnants can be explained with the spin-down scenario for the rotating super-Chandra mass WDs.