Revista Mexicana de Astronomía y Astrofísica

CCD Photometry of M15

2012-02-01T18:45:32-06:00

We present CCD observations of the galactic globular cluster M15, in the B and V lters. The cluster was reasonably covered, except in its northern region where our observations present a gap. We obtained a Hertzsprung-Russell (HR) diagram for each region observed, and later we produced a combined HR diagram containing more than 3000 stars. We generate a clean Colour Magnitude Diagram (CMD) and a Super Fiducial Line (SFL). Application of several methods and isochrone fitting leads us to obtain values for the metallicity [Fe/H]M15 ~ -2.16 ± 0.10, the reddening E(B - V )M15 ~ 0:11 ± 0.03, and a distance
modulus of [(m - M)0]M15 ~ 15:03.

Simple Model with Time-varying Fine structure "Constant''-Part II

2012-02-01T18:45:38-06:00

The extension of Dirac's LNH to cover cosmological and fine-structure timevarying "constants", and the rotation of the universe, is here analysed, including a "derivation" of the angular speed of the present universe, and of the inflationary phase. Controversial points in the present calculation are clarifi ed.

H91α Radio Recombination Line and 3.5 cm Continuum Observations of the Planetary Nebula NGC 3242

2012-02-01T18:45:38-06:00

We present high sensitivity H91 and 3.5 cm radio continuum observations toward the planetary nebula NGC 3242. The electron temperature determined assuming local thermodynamic equilibrium is consistent within ~10% with that derived from optical lines and the Balmer discontinuity. The line emission and the continuum emission have a very similar spatial distribution, suggesting that at this wavelength there is no other continuum process present in a signi cant manner. In particular, we conclude that emission from spinning dust is not important at this wavelength. In this radio recombination line the nebula presents a radial velocity structure consistent with that obtained from observations of optical lines.

IMF from infrared photometry of young stellar clusters in Taurus-Auriga and Orion

2012-02-01T18:45:38-06:00

We applied the extinction-disk-principal vectors approach to near infrared photometric data of the Taurus-Auriga region and Orion Nebula young stellar clusters. By assuming that the cluster age is represented by the median value of the age distribution we are able to derive the distribution of stellar masses. We showed that the resulting initial mass function (IMF) for these two young stellar clusters compares remarkably well and might be a robust representation of the IMF obtained by spectroscopic or photometric methods. The method also yields the extinction and disk contribution for each star. The overall extinction distribution for the Orion cluster is analyzed and compares well with previous work. The frequency of T Tauri stars with disks is about 50%.

A Photometric and Spectroscopic Evaluation of the Site at Tonantzintla Observatory

2012-02-01T18:45:38-06:00

Based on data obtained at the Observatorio Astronómico Nacional, Tonantzintla, an evaluation of the quality of the local sky is presented. The evaluation is carried out through an absolute CCD calibration to a set of standard stars in the field of M67 in the B, V , R and I Johnson-Cousins system and from Boller & Chivens long-slit spectroscopic observations of the local sky at various elevations. The sky brightness is estimated from our CCD frames yielding a mean value of 18.5 ± 0.6 mag arcsec⁻² . The mean atmospheric extinction curve behaves midway between the normal extinction and that related to volcanic outbursts. From the long-slit spectra of the sky at OAN-Tonantzintla, HgI and NaI lines of high and low pressure lamps are identi fied. These results allow us to justify a major upgrading of the observatory, to convert the OAN-Tonantzintla into the Laboratory for Astronomy Education both for UNAM and for other educational institutions in the center-south part of the country.

On the Precursors of Fossil Groups

2012-02-01T18:45:38-06:00

We compare the absolute magnitudes in the K-band of the brightest galaxies in clusters of Bautz-Morgan type I with those of the fossil group brightest galaxies. It is found that the brightest galaxies in fossil groups are on average fainter than the brightest galaxies in clusters. It is also shown that the brightness of the brightest galaxy depends on the cluster richness. It is concluded that the precursors of fossil groups were on average poor clusters.

Herbig-Haro objects around CG 30

2012-02-01T18:45:38-06:00

In this work we study Herbig-Haro objects located in the region around the head of the cometary globule CG 30. Two sets of optical images are presented. The first set was obtained with the 3.5 m New Technology Telescope in 1995 in three emission lines: H α, [S II] λ λ6731,6716 Å and [O II] λ3729 Å. The second set is an H image of the CG 30/31/38 complex obtained in 2006 with the 8 m Subaru telescope. A proper motion study of the HH objects in the region was performed using the H images from both epochs. Due to the high resolution of our images we were able, for the first time, to resolve the HH 120 object into ten knots and measure proper motions for some of them. We discovered several new HH objects which are best seen in our [S II] image as well as a large bipolar jet, HH 950, emerging from the head of CG 30. We suggest that two previously known submillimeter sources are the driving sources for the HH 120 and HH 950 flows. They could both be binary sources, because (1) the proper motion vectors of the HH 120 knots suggest that this object is actually composed of two outflows and (2) the structure of the HH 950
flow suggests that the direction of the jet axis has changed in the past.

Photoevaporation of a binary proplyd system

2012-02-01T18:45:38-06:00

We present 3D numerical simulations of photo-evaporation of a binary accretion disk system inside an H II region. The simulations take into account farand extreme-ultraviolet (FUV and EUV) radiation from a stellar source. We study both FUV dominated and EUV dominated models. FUV dominated models show a well de fined interproplyd shell in both H α emission and density maps, when the separation of the binary system is relatively large (~ 2 000 AU). For smaller separations (~ 200 AU), the interproplyd shell no longer develops. We show that an EUV model with a suitable choice of parameters increases the H emission of the interproplyd shell relative to the emission of the ionization fronts, in better agreement with the observations of the binary proplyd LV1.

The green potential of the San Pedro Mártir observatory

2012-02-01T18:45:38-06:00

Weather observations carried out between October 2004 and July 2008 at the Mexican Observatorio Astronómico Nacional (OAN) are analyzed. Humidity in April, May and June was less than 55% nearly 90% of the time. Wind speed was
larger at nightime and tended to decrease between March and November. Typical temperature variations during the night, for the entire day and for a whole year were about 2, 6 and 16ºC, respectively. The scale height or roughness length for the function relating wind speed and height above ground is between 0.55 and 0.67 meters. Normal activities associated to OAN produced somewhat more than 750 tons of COeq₂ a year, roughly 3 times more than a typical mid-scale industry in the district of Ensenada, where OAN is located. Wind energy could have been extracted to produce electricity ~ 60% of the time, being more bountiful during the night and in the winter and early spring months. Solar and wind energy seem plentiful enough to supply the entire energy needs of the observatory, some 110 kWh including transportation.

Age Estimation And Mass Functions of TTauri Stars in The Taurus Auriga Molecular Cloud

2012-02-01T18:45:38-06:00

In this work the present day mass functions (PDMF) of T-Tauri Stars (TTS) which are in the pre-main sequence (PMS) evolutionary phase of their evolution in the Taurus-Auriga Molecular Cloud Complex have been calculated. For this purpose, by applying our modi ed stellar evolutionary code, stellar models in the mass range 0.1 - 2.5 M ⊙ are used to determine the mass and age mass of TTS. The obtained mass function is compared with the mass function of Miller & Scalo (1979). The age found for TTS is around 1 - 3⁶ × 10 yr and the mass function is about 0.644±0.348. From these results, we have calculated the stellar birthrate as about 1.3 × 10⁻ ⁷ M ⊙ yr⁻¹ in this region.

A geometrical model for the catalogs of galaxies

2012-02-01T18:45:38-06:00

The 3D network originated by the faces of irregular Poissonian Voronoi polyhedra may represent the backbone on which the galaxies are originated. As a consequence the spatial appearance of the catalogs of galaxies can be reproduced. The selected catalogs to simulate are the 2dF Galaxy Redshift Survey and the Third Reference Catalog of Bright Galaxies. In order to explain the number of observed galaxies for a given flux/magnitude as a function of the redshift, the photometric properties of the galaxies should be carefully examined from both the astronomical and theoretical point of view. The statistics of the Voronoi normalized volume is modeled by two distributions and the Eridanus super-void is identi fied as the largest volume belonging to the Voronoi polyhedron. The behavior of the correlation function for galaxies is simulated by adopting the framework of thick faces of Voronoi polyhedra on short scales, while adopting standard arguments on large scales.

On the origin of the tailward velocity of O+ ions over the magnetic poles of Mars

2012-02-01T18:45:38-06:00

We numerically simulate the dynamics of a population of O⁺ ions of ionospheric origin picked-up by the solar wind in the dayside ionosheath of Mars. Their average velocity as they reach the magnetic polar regions of the planet is compared with in situ measurements of the Mars Express spacecraft. We find that the velocity of O⁺ ions measured over the magnetic poles of the planet, which is essentially tailward with very small y and z-components according to measurements, cannot be accounted for solely in terms of particle gyromotions. We suggest that the velocity of O⁺ ions over the magnetic poles of the planet is more probably the result of wave-particle interactions that mediate the transfer of momentum from the solar wind plasma to ionospheric plasma and newly born ions in the ionosheath.

Amplitude fluctuations in curvature sensing: comparison of two schemes

2012-02-01T18:45:38-06:00

The influence of amplitude fluctuations on the quality of phase reconstruction in curvature sensing is investigated. Two curvature schemes are compared: one with two symmetrically-defocused images (Roddier scheme) and one with a single defocused image (Hickson scheme). It is shown that the accuracy of phase reconstruction with the Hickson scheme is strongly a ected even by low-level amplitude fluctuations, while the Roddier scheme works well under quite strong amplitude fluctuations.

A Compact Radio Counterpart to the Energetic X-ray Pulsar Associated with the TeV Gamma-Ray Source J1813-178

2012-02-01T18:45:38-06:00

We report the detection of a time-variable, compact radio source coincident with CXOU J181335.1{174957, the X-ray pulsar near the center of the young radio supernova remnant G12.82{0.02, which overlaps the compact TeV source HESS J1813{178. The compact radio source, named VLA J181335.1{174957, was detected in 4.86 GHz VLA observations made in 2006. New VLA observations made in 2009 do not detect the source at a level 1.9±0.7 times (2.8σ) lower than that of 2006. We suggest that VLA J181335.1{174957 may be related to one of the recently detected classes of variable radio pulsars but cannot reach a firmer conclusion.

Planetary nebulae in the inner Milky Way: new abundances

2012-02-01T18:45:38-06:00

The study of planetary nebulae in the inner-disk and bulge gives important information on the chemical abundances of elements such as He, N, O, Ar, Ne, and on the evolution of these abundances, which is associated with the evolution of intermediate-mass stars and the chemical evolution of the Galaxy. We present accurate abundances of the elements He, N, S, O, Ar, and Ne for a sample of 54 planetary nebulae located towards the bulge of the Galaxy, for 33 of which the abundances are derived here for the rst time. The abundances are obtained based on observations in the optical domain made at the National Laboratory for Astrophysics (LNA, Brazil). The data show a good agreement with other results in the literature, in the sense that the distribution of the abundances is similar to that of those works.

HH jets aligned perpendicular to elephant trunks

2012-02-01T18:45:38-06:00

We consider a system of outflows ejected from low mass young stars embedded in the tips of elephant trunks. We assume that these outflows have axes which are intrinsically perpendicular to the axes of the host elephant trunks. We then derive the distribution function expected for the angle between the projections of the outflow and elephant trunk axes on the plane of the sky. These distribution functions are useful for interpreting the alignments (or lack thereof) observed between HH outflow and elephant trunk axes in photoionized regions.

ERRATUM

2012-02-01T18:45:38-06:00