Revista Mexicana de Astronomía y Astrofísica
The Revista Mexicana de Astronomia y Astrofisica, founded in 1974, publishes original research papers in all branches of Astronomy, Astrophysics and closely related fields. Two numbers per year are issued and are distributed free of charge to all institutions engaged in the fields covered by the RevMexAA.
Analysis of chromatic effects in the shift-and-add method
Chromatic effects in shift-and-add (SAA) adaptive systems are considered by means of computer simulations. Chromatic eects under investigations arise when measurements and corrections are performed in dierent wavelengths. A study of chromatic properties of SAA technique is useful for designing of SAA adaptive systems. Also it is important for data reduction of speckle-spectroscopic observations. The comparison of two approaches of low order adaptive corrections (SAA and tip-tilt) is presented. The advantages of SAA adaptive systems are outlined.
A new search for variable stars in the globular cluster NGC 6366
New CCD photometry of NGC 6366 has lead to the discovery of some variable stars. Two possible Anomalous Cepheids (or Pop II Cepheids), three long period variables, one SX Phe and one eclipsing binary have been found. Also, a list of 10 candidate variables is reported. The light curve of the RRab star, V1, has been decomposed into its Fourier harmonics, and the Fourier parameters were used to estimate the star's metallicity and distance; [Fe/H] = —0.87±0.14 and d = 3.2±0.1 kpc. It is argued that V1 may not be a member of the cluster but rather a more distant object. If this is so, an upper limit for the distance to the cluster of 2.8±0.1 kpc can be estimated. The P — L relationship for SX Phe stars and the identified modes in the newly discovered SX Phe variable, V6, allow yet another independent determination of the distance to the cluster, d = 2.7 ± 0.1 kpc. The MV-[Fe/H] relationship for RR Lyrae stars is addressed and the case of V1 is discussed.
Kinematic field of the S-shaped nebula N119 in the LMC
The nebula N119 in the Large Magellanic Cloud shows a very conspicuous morphology difficult to explain with classical models. The aim of the present paper is to provide kinematic data that could place constraints on the nature, formation and evolution of N119. The peculiar spiral shape of this nebula is also reflected in a peculiar radial velocity eld, showing several expansions of the faint laments which form dierent bubble-like regions, and another component whose origin remains unrevealed. N119 seems to contain three expanding bubble-shaped nebulae formed by the action of the stellar winds from Wolf-Rayet and O stars, and a possible remnant of an hypernova explosion. Indeed, we have detected for the rst time a bubble around the WR star Br 21, inside the N119 nebula.
The Helium and heavy elements enrichment of the Galactic Disk
We present chemical evolution models for the Galactic disk. We also present a new determination of X, Y , and Z for M17 a Galactic metal-rich H II region. We compare our models for the Galactic disk with the Galactic H II regions abundances. The ΔY/ΔO ratio predicted from the Galactic chemical evolution model is in very good agreement with the ΔY/ΔO value derived from M17 and the primordial helium abundance, Yp, taking into account the presence of temperature variations in this H II region. From the M17 observations we obtain that ΔY/ΔZ = 1.97±0.41, in excellent agreement with two ΔY/ΔZ determinations derived from K dwarf stars of the solar vicinity that amount to 2.1 ± 0.4 and 2.1 ± 0.9 respectively. We also compare our models with the solar abundances. The solar and Orion nebula O/H values are in good agreement with our chemical evolution model.
HH 30 is an edge-on disk around a young stellar object. Previous imaging with the Hubble Space Telescope has show morphological variability that is possibly related to the rotation of the star or the disk. We report the results of two terrestrial observing campaigns to monitor the integrated magnitude of HH 30. We use the Lomb-Scargle periodogram to look for periodic modulation with periods between 2 days and almost 90 days in these two data sets and in a third, previously published, data set. We develop a method to deal with short-term correlations in the data. Our results indicate that none of the data sets shows evidence for signicant periodic photometric modulation.
Bipolar clump ejection from a moving source
We present a model for the bipolar ejection of clumps from a source travelling within the surrounding, homogeneous ambient medium. The model has a full analytic solution, from which we derive parameters which can be directly compared with observations (e. g., the orientation of the line joining the two clumps and the separation between the clumps as a function of time). We compare the analytic model with a full 3D numerical simulation (with a parametrized cooling function), and find that the positions of the clumps obtained from the analytic model agree relatively well with the results from the numerical simulation.
The delayed contribution of low and intermediate mass stars to chemical galactic enrichment: An analytical approach
We find a new analytical solution for the chemical evolution equations, taking into account the delayed contribution of all low and intermediate mass stars (LIMS) as one representative star that enriches the interstellar medium. This solution is built only for star formation rate proportional to the gas mass in a closed box model. We obtain increasing C/O and N/O ratios with increasing O/H, behavior impossible to match with the Instantaneous Recycling Approximation (IRA). Our results, obtained by two analytical equations, are very similar to those found by numerical models that consider the lifetimes of each star. This delayed model reproduces successfully the evolution of the C/O—O/H and Y — O relations in the solar vicinity. This analytical approximation is a useful tool to study the chemical evolution of elements produced by LIMS when a galactic chemical evolutionary code is not available.
The mysterious Of?p class and the magnetic O-star θ1 Ori C: confronting observations
In recent years, the stars of the Of?p category have revealed a wealth of peculiar phenomena: varying line proles, photometric changes, and X-ray overluminosity are only a few of their characteristics. Here we review their physical properties to facilitate comparisons among the Galactic members of this class. As one of them has been proposed to resemble the magnetic oblique rotator θ1 Ori C, though with a longer period, this latter object is also included in our study to illuminate its similarities and differences with the Of?p category.
The interaction of a YSO outflow with the surrounding molecular cloud core
We present a thin shell, analytic model for an outflow ejected with an opening angle that increases as a function of time. This model predicts a cavity shape that broadens out with time, and pinches towards the out flow axis at a point that travels away from the outflow source. The motivation for this model is the set of observations of a bipolar cavity centered on Barnard 5 IRS 1 by Velusamy & Langer (1998), who suggest an interpretation for the observed structure in terms of a model such as the one that we have studied. We find that this observed structure could indeed be produced by an outflow of decreasing collimation as a function of time, provided that the mass loss rate has a value M_0 ≈ 3 × 10-6MΘ yr-1.
Kinematics of the Nebular Complex MH9/10/11 Associated with HoIX X-1
We report the results of our observations of the nebular complex MH9/10/11, associated with the ULX HoIX X-1, with a scanning Fabry-Pérot Interferometer. Two regions diering by their kinematics and line ratios may be distinguished, roughly corresponding to the bubble nebula MH9/10 and the fainter HII-region MH11. For MH9/10 we nd an expansion rate of 20 to 70 km s^-1 that is dierent for the approaching and receding parts. MH11 is characterised by a very low velocity dispersion (<~ 15 km s^-1) and nearly constant line-of-sight velocities. The properties of MH11 may be explained by photoionization of a gas with hydrogen density of ~0.2 cm^-3. The luminosity required for that should be of the order of 10^39 erg s^-1. A source of similar power is required to explain the expansion rate of MH9/10. Modelling results also indicate that the oxygen abundance in MH11 is about solar.
Energy and Angular Momentum of Dilaton Black Holes
Following a prior paper, we review the results for the energy and angular momentum of a Kerr-Newman black hole, and then calculate the same properties for the case of a generalised rotating dilaton of the type derived, without rotation, by Garfinkle et al. (1991, 1992). We show that there is, as far as it refers only to the energy and angular momentum, an interaction among the fields, so that, the gravitational and electromagnetic fields may be obscured by the strength of the scalar field.
Hydrodynamical Simulations of the Non-Ideal Gravitational Collapse of a Molecular Gas Cloud
In this paper we present the results of a set of numerical simulations aimed to study the gravitational collapse of a spherically symmetric, rigidly rotating, isolated, interstellar gas cloud. To account for the thermodynamics of the gas we use a barotropic equation of state (beos for brevity) that depends on the density ρ of the cloud and includes a critical density as a free parameter, ρcrit. During the early collapse, when ρ << ρ-crit, the beos behaves as an ideal gas equation of state. For the late collapse, when ρ ≥ ρ-crit, the beos includes an additional term that accounts for the heating of the gas due to gravitational contraction. We investigate the occurrence of prompt fragmentation of the cloud for which we use four dierent values of ρ-crit. We work with two kinds of collapse models, according to the initial radial density profile: the uniform and the Gaussian clouds.
A Photometric Study of the W UMa Type Eclipsing Binary V376 And
The new UBV photoelectric light curves of V376 And acquired at Ankara University Observatory in 2004 by the present authors and its BV light curves collected at Rozhen and Bucharest Observatories in 2003 (Dumitrescu et al. 2004) have been analysed and reanalysed, respectively, with the aim to derive physical parameters and to study the possible activity of the system. The solutions made by using Djuraševic's inverse-problem method in the simultaneous analysis of both seasonal light curves describe the V376 And system as a high overcontact conguration (f-over ~ 36% - 2004 and f-over ~ 55% - 2003) with relatively large temperature difference between components (ΔT = T-h — T-c ~ 880 — 840 K) which is characteristic for an A-type contact system. The light curve asymmetry can be explained by introducing the cool (solar type) spot region on the less massive, cooler, component.
The consequences of the conservation of the Jacobi constant (CJ) are studied here analytically for a circular binary system. The main result is that for every particle there are prohibited and allowed zones. This scheme is valid with the inclusion of interactions between the particles in the orbital plane of the binary system; this means that CJ and the allowed-prohibited configuration space are time-dependent. The formation and initial evolution of a disk around an isolated star is interpreted according to this work. We extend this model for the case where there is a small secondary star and argue that observational estimates of the ratio between circumprimary and circumbinary disk masses are consistent with a set of SPH simulations in which the ratio between the separation of the stars and the disk radius is the parameter that varies. GW Ori is used as an example.
Seeing and weather observations were conducted at 5 sites within the boundaries of the area reserved for astronomy at the Sierra de San Pedro Mártir National Park (SPM), for at least 15 nights at each one of these. Weather variables were measured using a Davis Weather Station and a Metek Ultrasonic Anemometer. Seeing information was collected with a NOAO RoboDIMM unit. Seeing and weather results were compared to those being delivered at the same time by the instrumentation of the Thirty Meter Telescope Project at the Observatorio Astronómico Nacional (OAN) at SPM. Seeing differences are small in most cases. We recommend a long term campaign at the easily accessible site Llano Alto 1, where we found that seeing may be slightly better.
Metallicity effects on the modified wind momentum of CSPN
Recent investigations on the central stars of planetary nebulae (CSPN) indicate that the masses based on model atmospheres can be much larger than the masses derived from theoretical mass-luminosity relations. Also, the dispersion in the relation between the modied wind momentum and the luminosity depends on the mass spread of the CSPN, and is larger than observed in massive hot stars. Since the wind characteristics probably depend on the metallicity, we analyze the effects on the modified wind momentum by considering the dispersion in this quantity caused by the stellar metallicity. Our CSPN masses are based on a relation between the core mass and the nebular abundances. We conclude that these masses agree with the known mass distribution both for CSPN and white dwarfs, and that the spread in the modied wind momentum can be explained by the observed metallicity variations.
Chemical Composition in Fast Rotators Main Sequence Stars
Using public data of the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project (UVES POP) the projected rotational velocities, v sin i, for 16 stars in the field of the galactic cluster IC 2391 (o Vel Cluster) were obtained using the method of the Fourier transform (FT). We found that only 12 of these objects are cluster members and separating them in two sets (main sequence stars and evolved stars) a correlation of the rotation velocity with the effective temperature was found, indicating a nearly equal orientation of the rotation axis for the member stars. The ratios N/C and O/C obtained for the main sequence stars increase with v sin i and show evidence of mixing induced by rotation.
Velocity Structure in the Orion Nebula. II. Emission Line Atlas of Partially Ionized to Fully Ionized Gas
We present an atlas of three-dimensional (position-position-velocity) spectra of the Orion Nebula in optical emission lines from a variety of different ionization stages: [O I] 6300Å, [S II] 6716,6731Å, [N II] 6584Å, [S III] 6312Å, Hα 6563Å, and [O III] 5007Å. These transitions provide point to point information about the physical structure and kinematics of the nebula at an effective resolution of 3" × 2" × 10 km s⁻¹, clearly showing the large scale behavior of the ionized gas and the presence of localized phenomena such as Herbig-Haro outflows. As an example application of the atlas, we present a statistical analysis of the widths of the Hα, [O III], and [N II] lines that permits a determination of the mean electron temperature in the nebula of (9200 ± 400) K. We also find, in contradiction to previous claims, that the non-thermal line broadening is not significantly different between recombination lines and collisional lines.
An atlas of synthetic line profiles of planetary nebulae
We have constructed a grid of photoionization models of spherical, elliptical and bipolar planetary nebulae. Assuming different velocity fields, we have computed line profiles corresponding to different orientations, slit sizes and positions. The atlas is meant both for didactic purposes and for the interpretation of data on real nebulae. As an application, we have shown that line profiles are often degenerate, and that recovering the geometry and velocity field from observations requires lines from ions with different masses and different ionization potentials. We have also shown that the empirical way to measure mass-weighted expansion velocities from observed line widths is reasonably accurate if considering the HWHM. For distant nebulae, entirely covered by the slit, the unknown geometry and orientation do not alter the measured velocities statistically. The atlas is freely accessible from internet. The Cloudy-3D suite and the associated VISNEB tool are available on request.
HII regions in NGC 5055. II. Physical Properties
In this paper, using CCD observations of the galaxy NGC 5055 in the emission lines of H\alpha and H\beta (Rozas 2007), together with CCD observations in the narrow- band filters of [OII], [OIII], [SII], and S[III] lines we have calculated the equivalent widths, excitations, ionization hardness, ionization parameters and metallicities for the regions catalogued in Rozas (2007).
Flat Central Density Profiles from Scalar Field Dark Matter Halos
Scalar fields endowed with a cosh potential behave in the linear regime, exactly as the cold dark matter (CDM) model. Thus, the scalar eld dark matter (SFDM) hypothesis predicts the same structure formation as the CDM model. This means that CDM and SFDM are equivalent from the cosmological point of view. The free parameters of the SFDM model are determined by cosmological observations. In previous work we showed that if we use such parameters, the scalar field collapses forming stable objects with a mass around 10¹² M⊙. In the present work we use analytical solutions of the flat and weak field limit of the Einstein-Klein-Gordon equations and show that the SFDM density prole corresponds to a halo with an almost at central density and that it coincides with the CDM model in a broad outer region. This result could solve the problem of the density cusp DM halo in galaxies without any additional hypothesis, thus supporting the viability of the SFDM model.
Orbital Elements for BU 1240 AB. Nature of the C and D Components
New orbital parameters and masses for WDS 05386+3030 = BU 1240 AB were determined prompted by the large residuals seen in recent speckle measurements from 1985. A combined solution of graphical (to determine preliminary parameters) and analytical methods was used. The preliminary orbit was rened using the differential correction method by Heintz. The physical characteristics of the C and D components were studied using BVIJHK photometry, historical astrometry and kinematical data. Several criteria indicate a physical nature for C and an optical nature for D.
Photometric and spectroscopic study of seven Shakhbazian compact galaxy groups
The results of the detailed spectroscopic and photometric study of seven Shakhbazian compact groups: ShCG 285, ShCG 289, ShCG 322, ShCG 323, ShCG 327, ShCG 330, and ShCG 346, are presented. We determined redshifts of member galaxies and radial velocity dispersions of groups. We studied also the distribution of the surface brightness of member galaxies in R and determined their morphological types. We found that, as in previously studied ShCGs, some group members are interacting or are even in the process of merging. We determined physical parameters of groups: virial masses, luminosities, mass-to-luminosity ratios, and the crossing times. On the basis of the results obtained in this and our previous works, the general properties of 37 ShCGs are discussed. It is shown that about 75% of member galaxies are of E and S0 type.
On the nature of the Open Clusters in the direction of NGC 6882/5
Unpublished uvby-β photoelectric photometry of the open cluster NGC 6882/5 is presented. Utilizing already tested distance determinations through photometric techniques, it is found that there are at least two distinct star accumulations in the direction of the open cluster NGC 6882/5. A brief discussion is made of the nature of the previously found short period variables.
Radial Dependence of Extinction in Parent Galaxies of Supernovae
The problem of extinction is the most important issue to be dealt with in the process of obtaining true absolute magnitudes of core-collapse (including stripped-envelope) supernovae (SNe). The plane-parallel model, widely used in the past, was shown not to describe extinction adequately. We try to apply an alternative model which introduces radial dependance of extinction in parent galaxies of supernovae. For calculating extinction in our Galaxy we use two different methods and compare the results obtained. Our analysis is primarily focused on a chosen sample of stripped-envelope SNe (Ib/c) for which we nd intrinsic peak absolute magnitude M^0_B = -17.80 ± 0.43.
Kinematics and Velocity Ellipsoid of M Giants
To study the kinematics of M giant stars (luminosity class III) use is made of 1,532 stars with proper motions taken from the Hipparcos catalog, of which 480 have radial velocities. Stars farther off than 700 pc were excluded because they induce a noticeable tilt in the distribution of the stars. Various solutions were performed, and the one calculated by the robust L1 norm was taken as the best. Kinematical parameters and the coefficients of the velocity ellipsoid are solved for simultaneously. The results obtained are reasonable: solar velocity of 24.20±0.70 km s ⁻¹; Oort's constant's, in units of km s ⁻¹ kpc ⁻¹, A = 16.86 ± 2:78 and B = -6.34 ± 2.56, implying a rotational velocity of 197.27±26:80 km s ⁻¹. The velocity ellipsoid is tilted considerably with respect to the Galactic plane in the y direction.
Haystack Observations of CS and CH3OH Toward Star Forming Regions
We report ¹²CS J= 1 → 0 observations toward 20 star forming regions conducted with the MIT 37m Haystack telescope. Three of the sources were also observed in the ¹³CS J= 1 → 0 line, and five sources where observed in the CH₃OH JK = 70 → 6¹ A+ transition at 44 GHz. We detected ¹³CS and CH₃OH emission toward all sources observed, and ¹²CS emission toward 19 of the 20 sources in the sample, 11 of which are new detections. We found a strong correlation between the ¹²CS FWHM and the source distance, indicating the potential use of ¹²CS J= 1 → 0 emission as a tool to estimate distances to star forming regions. We also report detection of CH₃OH 44 GHz maser variability in most of the observed sources.
Determination of the IMF in the LMC Stellar Cluster NGC 2156
We present a study on the IMF of the stellar cluster NGC 2156 in the LMC from deep HST-WFPC2 images in the bands F555W and F814W. The study is part of a larger program to investigate whether the IMF at low stellar masses is dependent on local conditions by observing young globular clusters in the LMC and the SMC. We detected stars down to a limiting magnitude of m555 = 26, which corresponds to stellar masses of ~ 0:6 M at the distance of the LMC (50:11 Kpc). A comparison of the cluster CMD with theoretical isochrones indicates an age of 49±5 Myr. We performed a completeness analysis and determined the background stellar contamination to correct the observed LF and derive the MF of the cluster using the standard ML-relation for main sequence stars. Given the fact that the cluster is very young, the present day MF is expected to be a good approximation to the IMF.
New insights into the nature of the SMC WR/LBV binary HD 5980
We present the results of optical wavelength observations of the unusual SMC eclipsing binary system HD 5980 obtained in 1999 and 2004{2005. Radial velocity curves for the erupting LBV/WR object (star A) and its close WR-like companion (star B) are obtained by deblending the variable emission-line proles of NIV and NV lines. The derived masses MA = 58 - 79M and MB = 51 - 67M, are more consistent with the the stars' location near the top of the HRD than previous estimates. The presence of a wind-wind interaction region is inferred from the orbital phase-dependent behavior of He I P Cygni absorption components. The emission-line intensities continued with the declining trend previously seen in UV spectra. The behavior of the photospheric absorption lines is consistent with the results of Schweickhardt (2000) who concludes that the third object in the combined spectrum, star C, is also a binary system with PstarC ~96.5 days, e=0.83.
A dynamical model for the spiral galaxy NGC 3359
In this work we have determined a dynamical model for NGC 3359. This is a strongly barred spiral galaxy with a complex structure, within which we can see an annular zone of intense star formation. In this work we present self consistent numerical simulations of molecular gas in NGC 3359; and using the potential derived from an I band image, we attempt to find the parameters responsible for the kinematics and morphology of the observed gas. The best results are obtained for a two pattern speed model: the central region (up to 15") corresponding to the nuclear bar which rotates with a Ωs=100 km s⁻¹ kpc⁻¹; and the main bar + outer spiral, decoupled from the nuclear region, which rotates with a angular velocity, Ωp = 27 km s⁻¹ kpc⁻¹. The model successfully reproduces the complex structure in H\alpha of the galaxy in the internal 20" zone, which cannot really be explained with a unique mode pattern.