Showing papers in "Revista Mexicana De Astronomia Y Astrofisica in 2003"

Galaxy Star Formation as a function of Environment

Abstract: We study the galaxy star formation rate (SFR) as a function of environment using the SDSS EDR data. We nd that the SFR is depressed in dense environments (clusters and groups) compared to the eld. We nd that the suppression of the SFR starts to be noticeable at around 4 virial radii. We nd no evidence for SF triggering as galaxies fall into the clusters. We also present a project to study these eects in cluster pairs systems where the eects of lamen ts and large scale structure may be noticeable.

The Manchester Echelle Spectrometer at the San Pedro Mártir Observatory (MES-SPM)

Abstract: The performance of the second version of the Manchester Echelle spectrometer is described when combined with the San Pedro Martir, 2.1 m telescope. The simplicity but eectiv eness of the optical design is explained as a consequence of the spectrometer’s dedication to a narrow range of astrophysical problems i.e., where spatially resolved line proles are required from faint, extended sources at high signal-to-noise ratios. The improvement in operational eciency is demonstrated as a consequence of the recent (2000) upgrade of the control system. Finally, comparisons are made with the performance of competitive stepped Fabry-Perot interferometers on similar problems. The complementarity of spectrometers of dieren t types is emphasized.

Bubble nebulae around ultraluminous x-ray sources

Abstract: RESUMEN La naturaleza de las fuentes de rayos-X ultraluminosas (ULX) externas a los n ucleos de galaxias cercanas contin ua ser un misterio puesto que la cantidad de radiaci on a altas energ as, si fuera isotr opica, rebasar a el l mite de Eddington incluso de los hoyos negros estelares m as masivos. Muchas de las fuentes de rayos-X ultraluminosas est an rodeadas por nebulosas de emisi on, las cuales muestran indicaciones de ionizaci on tanto por choques como por rayos-X. Se pueden utilizar las nebulosas relativamente compactas ionizadas por rayosX para inferir de manera independiente las luminosidades y por lo tanto excluir posibles efectos de enfoque hacia la visual. Las nebulosas m as grandes tipo burbuja alcanzan di ametros de algunas centenas de parsecs y proporcionan informaci on importante acerca de la formaci on y/o historia de p erdida de masa de las ULX. Se~ la relaci on cercana que hay con los microcuasares y el sistema SS 433, anteriormente unico, con su nebulosa de radio W 50.

Mid-Infrared Detection of a Hot Molecular Core in G29.96-0.02

Abstract: We present high angular resolution (~05) 10 and 18 ?m images of the region around G29.96-0.02 taken from the Gemini North Observatory 8 m telescope using the mid-infrared imager and spectrometer OSCIR. These observations were centered on the location of a group of water masers, which delineate the site of a hot molecular core believed to contain an extremely young massive star. We report here the direct detection of a hot molecular core at mid-infrared wavelengths at this location. The size and extent of the core at 18 ?m appears to be very similar to the morphology as seen in integrated NH3 maps. However, our observations indicate that the mid-infrared emission may not be exactly coincident with the NH3 emission.

Three-Component Modeling of C-Rich AGB Star Winds

Abstract: The AGB stars are complex systems with interacting radiation, gas and dust processes, all of which an accurate model has to describe properly. Our wind model is based on time-dependent radiation-hy ...

A revised calibration of the mv {w (o i 7774) relationship using hipparcos data: its application to cepheids and evolved stars 1

Abstract: A new calibration of the MV {W (O I 7774) relationship has been calculated using better reddening and distance estimates for a sample of 27 calibrator stars of spectral types A to G, based on accurate parallaxes and proper motions from the Hipparcos and Tycho catalogues. The present calibration predicts absolute magnitude with accuracies of 0:38 mag for a sample covering a large range of MV , from 9:5 to +0:35 mag. The color term included in a previous paper has been dropped since its inclusion does not lead to any signican t improvement in the calibration. The variation of the O I 7774 feature in the classical cepheid SS Sct has been studied. We calculated a phase-dependent correction to random phase OI feature strengths in Cepheids, such that it predicts mean absolute magnitudes using the above calibration. After applying such a correction, we could increase the list of calibrators to 58 by adding MV and O I triplet strength data for 31 classical Cepheids. The standard error of the calibration using the composite sample was comparable to that obtained from the primary 27 calibrators, showing that it is possible to calculate mean Cepheid luminosities from random phase observations of the O I 7774 feature. We use our derived calibrations to estimate MV for a set of evolved objects to be able to locate their positions in the HR diagram.

Dynamics of the Molecular Jets in the Archetypical Preplanetary Nebula, IRAS 16342-3814

Abstract: That strong jets can be launched at very early stages in preplanetary nebulae is nowhere better evidenced than in the class of \water fountain nebulae": systems in which very high-velocity H2O masers occur along the polar axis. The most extreme member known in this class is IRAS 16342 3814, which displays H2O maser emission at radial velocities of 160 km s 1 relative to the central, systemic velocity. It thus places the strongest constraints on the timing and kinematics of the polar outo ws in such systems. Here, we describe this class of object, and report on the rst results from our VLBA study of water masers in IRAS 16342. In this ongoing study, the proper motions of the masers, when combined with their radial velocities, should eventually provide a rather complete picture of the evolution of the jet dynamics.

About the emission line sequence of h ii galaxies

Abstract: We consider 400 H ii galaxies in which the oxygen abundances were obtained by electron temperature based methods. We split the sample in three metallicity bins. In each bin, a narrow sequence is found not only in pure emission line ratio diagrams but also in terms of H equivalent width, indicating the existence of an evolutionary sequence. Our diagrams show unambiguously the existence of an evolution on a timescale of a few Myr. We compare the observed sequences with photoionization models of appropriate metallicity. In order to understand the evolution of H ii galaxies one needs to consider the evolution of the gas as well as that of the stars. The observations require EW(H ) to decrease more rapidly than predicted by the passive evolution of a starburst. A photoionized adiabatic expanding bubble with a covering factor decreasing with time reproduces most diagrams. However, the question of the heating of H ii galaxies and the origin of the nebular He ii 4686 emission are not settled. We nd evidence for self-enrichment in nitrogen on a time scale of several Myr.

Twenty years of weather and observing statistics in san pedro m artir, baja california, mexico

Abstract: Statistics are presented covering 20 years of use of the 2.1m telescope of the Observatorio Astron omico Nacional at San Pedro M artir, Baja California, Mexico. As in the previous compilation, the fractional number of nights with totally clear, partially clear and mostly cloudy skies were determined. The fraction of nights lost due to bad weather was 22.2% in the period July 1982 to December 2002. From January 1984 to December 2002, 63.1% of the nights were of \photometric" quality and 80.8% were of \spectroscopic" quality. During the past seven years of \drought" in the area, the fraction of photometric quality nights increased to 73.5%, but the fraction of spectroscopic nights remained similar to previous years. The gures are similar to those reported for the Chilean sites and are better than those for Northern Hemisphere observatories.

Wolf-Rayet Central Stars and the Binary Evolution Channel

Abstract: Resumen en: Single star evolutionary calculations have recently succeeded in reproducing the composition of the hydrogen deficient Wolf-Rayet (WR) central stars of p...

The Circum-Galactic Environment of LINERs

Abstract: Resumen en: In this paper, we study the circumgalactic environment of LINER host galaxies, in a sample of 166 objects drawn from a Multifrequency Catalogue of LINERs...

Stellar Outflows with New Tools: Advanced Simulations and Laboratory Experiments

Abstract: In this contribution we provide a brief overview of new numerical results describing the evolution of clumpy o ws as well as new studies of magnetized winds/jets. In addition, we report on a new approach to studying these phenomena: direct laboratory experiments. Recent advances in the use of \high energy density" laboratory devices now allows researchers to produce scalable plasma o w experiments relevant to hypersonic astrophysical jets and shock-clump interactions in the context of circumstellar outo ws.

A primer for the San Pedro Mártir observatory

Abstract: Resumen es: The Observatorio Astronomico Nacional is run and operated by the Instituto de Astronoma of the National Autonomous University of Mexico. It is locate...

Optical-turbulence and wind profiles at san pedro m artir

Abstract: Results of monitoring optical{turbulence proles and velocity of the turbulence layers at San Pedro M artir, Mexico, are presented. The data were collected during 11 nights in April{May 1997 and 16 nights in May 2000 using the Generalized Scidar of Nice University installed on the 1.5{m and 2.1{m telescopes. The statistical analysis of the 6414 turbulence proles obtained shows that the seeing produced by the turbulence in the rst 1.2 km, not including dome seeing, at the 1.5{m and the 2.1{m telescopes have median values of 0. 00 63 and 0. 00 44, respectively. The dome seeing at those telescopes have median values of 0. 00 64 and 0. 00 31. The turbulence above 1.2 km and in the whole atmosphere produces seeing with median values of 0. 00 38 and 0. 00 71. The temporal correlation of the turbulence strength drops to 50% in time lags of 2 and 0.5 hours, approximately, for altitudes below and above 16 km above sea level, respectively. The turbulence above 9 km remained notably calm during 9 consecutive nights, which is encouraging for adaptive optics observations at the site. The 3016 proles of the turbulent{layer velocity that are analyzed show that the fastest layers are found between 10 and 17 km, where the tropopause and the jet stream are located, with median speed of 24.4 m s 1 . In the rst 2.2 km and above 17 km, the turbulent layers move relatively slowly, with median speeds of 2.3 and 9.2 m s 1 . The median of the wavefront coherence{time is 6.5 ms, in the visible. The results obtained here places San Pedro M artir among the best suited sites for installing next generation optical telescopes.

Wavefront outer scale measurements at San Pedro Martir Observatory. Its impact on Adaptive Optics performances

Abstract: The rst measurements of the spatial coherence outer scale L0 at the Observatorio Astron omico Nacional at San Pedro M artir, Mexico, are reported. This parameter was measured with the Generalized Seeing Monitor of Nice University, France. A log{normal distribution is found with a median value of 27.0 m. The importance of L0 in the derivation of adaptive optics (AO) performances is discussed. It is shown that low L0 values boost the corrective ability of low{order AO, but have almost no eect on high{order AO performances.

H2 velocity structure in HH 211

Abstract: H. L. Johnson, 1964, BOTT, 3, 25, 305 established standard stars for his JKL and M photometry, and developed a calibration that enabled him to determine bolometric corrections and effective temperatures. In many ways Johnson anticipated the developments that were about to come forth. Many of Johnson’s observations of the bright stars might still be the best available because astronomy has concentrated heavily on fainter objects following the end of Johnson’s career.

Orbital Dynamics Analysis of Binary Systems in Mass-Loss Scenarios

Abstract: We analyze the dynamics of binary systems with time-dependent mass loss and periastron eect|i.e., a supposed enhanced mass loss during periastron passages|by means of analytical and numerical techniques. In this way, we study the variation of orbital elements in terms of three small parameters, which describe the time-dependent mass loss ( 1, 2) and the mass loss by periastron eect ( ). It is demonstrated that the latter gives rise to secular variations in some orbital elements: eccentricity, semi-major axis and period. Lastly, we suggest that some of the anomalous behavior observed in some close binaries can be explained by taking into account the periastron eect. As a demonstration some practical applications are also included.

Contribution of the surface layer to the seeing at san pedro m artir: simultaneous microthermal and dimm measurements

Abstract: Results from experiments measuring the contribution of the surface layer to the optical seeing at the Observatorio Astron omico Nacional at San Pedro M artir (OAN{SPM) are reported. Microthermal sensors placed at 7 levels on a 15-m-high instrumented mast were used to measure the structure constant of the refractive index C 2 n . The integrated seeing parameter was measured with a Dieren tial Image Motion Monitor during 23 nights. Log{normal statistics were found for the seeing with mean of 0.98 00 and median value 0.84 00 . The contribution of the surface layer (2.3 to 15 m) to the total optical turbulence has a mean value of 16%, which corresponds to a degradation of 10% of the total seeing. These values are similar to those found in other observatories around the world, suggesting that the presence of trees in the OAN{SPM does not have a signican t eect on the surface layer seeing. Further studies should provide a conrmation of this tendency.

Optical line profile variability of the b1+neutron star binary system ls i +65 010 (2s 0114+650)

Abstract: We present high-resolution spectroscopic observations of the massive X-ray binary system LS I +65 010 (2S 0114+650) in the optical wavelength region. A correlation between equivalent width and radial velocity of photospheric absorption lines is found. The systemic velocity, inferred from the weaker lines, is Vhelio 31 5 km s 1 , which, if attributed solely to the Galactic rotation curve, implies that LS I +65 010 lies within 3 kpc from the Sun. The ISM Na I D lines display 2 resolved high velocity components at Vhelio 70, 48 km s 1 , possibly associated with gas surrounding the binary system, in addition to the 24 and 8 km s 1 ISM features due to the Orion and Perseus arm regions, respectively. Strong photospheric line prole variability is present on a night-to-night timescale, with He I 5875 A displaying an additional blue-shifted absorption in some of the spectra, similar to what is observed in the optical counterpart of Vela X-1. A connection between the extended blue wing and X-ray maximum is suggested. Short timescale variations in line proles are detected on only two nights, but the evidence that these variations occur on the 2.78 hour X-ray aring period is marginal.

Near ground wind simulations by a meso-scale atmospherical model for the extremely large telescopes site selection

Abstract: Currently, many Extremely Large Telescopes (ELTs: [30 100] m size) projects exist. Because of the huge size of such instruments, the selection of an optimal site having a low wind intensity at ground level is a fundamental priority to assure the telescope stability. Wind intensity estimations provided by the general circulation models of the meteorological world centres (such as the ECMWF) are not reliable, because of their low horizontal resolution (2 2:5 ). In this paper we test the ability of a non-hydrostatic meso-scale model (Meso-Nh), having a horizontal resolution of 1 km, in reconstructing the near ground wind intensity (NGW) measured at Paranal, Chile and Maidanak, Uzbekistan, and the ability of the model to discriminate between the two sites. Measurements of the NGW taken during some years at the two sites show a typical wind speed dierence of 4 { 5 m/s. In this paper, NGW measurements from 20 25 nights at each site are compared with simulations and a statistic analysis is made. Our conclusion is that the Meso-Nh model can discriminate between the two sites. On the contrary, the analyses and/or forecasts provided by the general circulation models cannot. The limitations of this study are discussed, and some procedures to by-pass these limitations are suggested.

Recent Advances in the Collapse and Fragmentation of Turbulent Molecular Cloud Cores

Abstract: Resumen en: Observations of stars in the vicinity of the Sun show that binary systems are prevalent and appear to be a general outcome of the star-formation process...

The Wind Properties of Eta Carinae

Abstract: We perform X-ray spectral fits to a recently obtained Chandra grating spectrum of η Carinae, one of the most massive and powerful stars in the Galaxy, and which is strongly suspected to be a colliding wind binary system. The good fit that we obtain gives us further confidence in the binary hypothesis, and we find Ṁ ≈ 2.5 × 10 M yr −1 for the mass-loss rate of η Car. In recent years, there has been growing evidence that the superluminous star η Carinae (HD 93308, HR4210) may be a binary (Damineli 1996; Duncan et al. 1995; Lamers et al. 1998; Corcoran et al. 2000). The presence of an early-type companion means that a powerful wind-wind collision will contribute to the observed emission, and is consistent with observed X-ray and radio variability. In addition, the X-ray emission from η Car is unlike any of the other single stars observed so far at high energies and dispersion and shares some common features with other colliding wind binaries. A binary interpretation remains somewhat controversial, however, not least because recent STIS spectra did not confirm the predicted variations in the radial velocity of the emission lines (Davidson et al. 2000). To test the binary hypothesis, and to obtain accurate estimates of the wind parameters of each star, we have recently fitted a Chandra grating spectrum against a grid of synthetic spectra calculated from a range of hydrodynamical models of the wind-wind collision (see Pittard & Corcoran 2002 for further details). As η Carinae has a relatively slow wind, the majority of the hard X-ray emission arises from the shocked wind of the companion. In our calculations we fix the wind speed of η Car to 500 km s and the wind momentum ratio, η = (Ṁ2v∞,2)/(Ṁ1v∞,1), to 0.2, as suggested from models of the X-ray eclipse. Our best-fit to the data (Figure 1) yields the following wind parameters for the companion: Ṁ2 ≈ 10 M yr , v∞,2 ≈ 3000 km s . With our previous assumptions this implies that the mass-loss rate of η Carinae is Ṁ1 ≈ 2.5 × 10 −4 M yr . This is smaller than typically inferred (e.g., Hillier et al.

Magnetic Accretion Onto T Tauri Stars

Abstract: Resumen en: High resolution spectroscopy of photospheric absorption lines, particularly in the infrared, reveals the presence of magnetic fields on T Tauri stars. Hi...

Submillimeter Observations of Cassiopeia A

Abstract: We present an 850 m image of the young supernova remnant Cas A obtained with SCUBA on the JCMT. The morphology of the emission is very similar to that at longer wavelengths, in the radio domain, implying that synchrotron remains the dominant emission mechanism at sub-millimeter wavelengths. The total ux of Cas A measured at 850 m does present a fairly large excess over the ux expected from synchrotron emission alone (as extrapolated from lower frequency data), but it remains unclear whether this excess is real and reects the presence of large amounts of cold dust, or if it is an artifact of the observing technique.

LIRIS (long-slit intermediate resolution infrared spectrograph) project status

Abstract: LIRIS is a near-IR intermediate resolution spectrograph with added capabilities for multi-object, imaging, coronography, and polarimetry. This instrument is now being constructed at the IAC, and upon complexion will be installed on the 4.2m William Herschel Telescope at the Observatorio del Roque de Los Muchachos. The optical system uses lenses and is based on a classical collimator/camera design. Grisms are used as the dispersion elements. The plate scale matches the median seeing at the ORM. The detector is a Hawaii 1024 X 1024 HgCdTe array operating at 60K.

Otelo: A proposal for a GTC key project

Abstract: OTELO (OSIRIS Tunable Emission Line Object Survey) is the GTC Key Project that will allow an optimal exploitation of the Spanish Day One GTC instrument OSIRIS with a high scientic output and international impact. The survey will be made using tunable lters, a unique feature of OSIRIS in 8{10 m telescopes, to do co-mobile tomography at a depth enabling measurements to be made of the faintest emission line sources, while scanning a volume of the Universe containing a statistically signican t sample of such objects. With this technique, and given the high sensitivity gained by the use of the tunable lters, OTELO will be the deepest and richest survey of emission line objects to date, providing an enormous amount of valuable data to tackle a wide variety of rst-rank scientic projects.

Dynamic Shocks in the Inhomogeneous Environment of the Cygnus Loop

Abstract: The inhomogeneous interstellar medium determines the evolution and appearance of the Cygnus Loop supernova remnant. Specifically, interactions of the shock front with large interstellar clouds produce nearly all of this remnant’s emission at X-ray and optical wavelengths. Observations with the Chandra X-ray Observatory and the Hubble Space Telescope reveal the dynamic blast wave and the detailed structure of individual clouds. In some cases, notably the western limb, a simple one-dimensional model of the interaction is sufficient, whereas other regions require discrimination of multiple projections or more complex models. The Cygnus Loop ultimately serves as a useful probe of the interstellar medium and as one of the best existing laboratories of shock physics.

A study of the variability of water maser emission in a sample of young stellar objects

Abstract: We present results of water maser observations in a sample of young stellar objects. The observations were made using the Haystack 37 m antenna during a span of time of about eight months. The sample was selected to study the variability of the water maser emission in young sources with far-infrared luminosities between 260 and 2:5 10 4 L . The results are shown in a series of plots that allow the analysis of the variation of the maser emission and to discuss the global properties of the sample. The results show that in all the observed sources the water maser emission varies with time. Based on the observed variability, the sample shows two kinds of behavior. About half of the sources show large variations in the peak ux density of at least one feature (by more than an order of magnitude) in time spans between one and several months, while in all the sources there is more than one feature where the changes in peak ux density are smaller (by less than a factor of 10) but in similar time scales. Finally, the variability of the observed water maser emission does not show a clear periodicity pattern in time and we do not nd a clear relationship between the luminosity of the sources and the water maser variability. From a statistical point of view, the H2O maser variability can be described as due to small (10%) Gaussian uctuations in the line opacity.