RevMexAA: Abstracts of Recently Received Papers


January 14, 2003

2003: December November October September August July June May April March February January

2002: December November October September August July June May April March February January


January 2003


Photometric and spectroscopic study of Shakhbazian compact galaxy groups ShCG 31, ShCG 38, ShCG 43, and ShCG 282

Hrant M. Tovmassian 1, H. Tiersch 2, S. G. Navarro 4, V. H. Chavushyan 1, Gaghik H. Tovmassian 5, A. S. Amirkhanian 6, S. Neizvestny 7

1INAOE, México.

2Sternwarte Königsleiten, Germany.

3IAC, Spain.

4OAN, UNAM, Mxico.

5BAO, Armenia.

6SAO RAS, Russia.

hrant@inaoep.mx

Received: 2003 January 8

Abstract: Shakhbazian compact galaxy groups are the most dense configurations known. A few years ago we commenced a detailed spectral and photometric study of these groups. In this paper we present the results of investigation of groups ShCG 31, ShCG 38, ShCG 43, and ShCG 282. The redshifts of member galaxies, the results of the BVR photometry, the surface brightness - effective radius curves, the estimated masses, luminosities, and the mass-to-luminosity ratios of groups, and also some dynamical parameters, as the radial velocity dispersion and the crossing time are presented. The studied ShCGs consist mostly of elliptical and lenticular galaxies. It is shown that some galaxies in groups are in the process of interaction.


CCD Photometry of the Open Clusters NGC 2658,
NGC 2849, and NGC 3247

Javier A. Ahumada 1

Observatorio Astronómico, Universidad Nacional de Córdoba, Argentina

1Visiting Astronomer, University of Toronto Southern Observatory, and Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan.

javier@oac.uncor.edu

Received: 2003 January 6

Abstract: We present CCD photometry of the galactic open clusters NGC 2658, NGC 2849 and NGC 3247. By means of the comparison between the observed cluster sequences and theoretical isochrones of solar metallicity, we derive the following parameters: NGC 2658, E(B V ) = 0.37 ± 0.03, log age = 8.35 ± 0.05, and r = 4.75 ± 0.30 kpc; NGC 2849, E(B V ) = 0.41 ± 0.03, log age = 8.90 ± 0.05, and r = 5.50 ± 0.35 kpc; NGC 3247, E(B V ) = 0.31 ± 0.03, log age = 8.35 ± 0.05, and r = 2.20 ± 0.15 kpc.



December 2002


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

J. Meaburn

Jodrell Bank Observatory

and

J. A. López, L. Gutiérrez, F. Quiróz, J. M. Murillo, J. Valdéz & M. Pedrayez.

Instituto de Astronomia, Campus Ensenada

jm@ast.man.ac.uk

Received: 2002 December 2

Abstract: The performance of the second version of the Manchester Echelle spectrometer is described when combined with the San Pedro Martir, 2-m telescope. The simplicity but effectiveness 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 profiles are required from faint, extensive sources at high signal to noise ratios.

The improvement in operational efficiency 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 different types is emphasized.



November 2002


H 2 Velocity Structure in HH 211

Luis Salas

Instituto de Astronomía, UNAM, Ensenada, B.C., México

and

Irene Cruz-González and Margarita Rosado

Instituto de Astronomía, UNAM, D.F., México

salas@astrosen.unam.mx

Received: 2003 November ??

Abstract: We describe the velocity structure of the molecular outflow HH 211 in the 2.12 μm line of H 2. Observations were obtained using an IR Fabry-Pérot interferometer with a spectral resolution of 24 km s 1. It is observed that the eastern lobe of the outflow is blue-shifted while the western side is red-shifted. Most of the emission originates at low velocities, in agreement with the flux-velocity relation of Salas & Cruz-González (2002), but these velocities are in general higher than the low velocities observed in CO. There is also evidence of the high velocities that trace the molecular jet, in both CO and SiO, and these high velocities in H 2 occur closer to the central axis of the outflow. These arguments lead us to the conclusion that H 2 coexists with CO in the molecular outflow, as opposed to the view that H 2 emission arises in the shocked quiescent medium. The jet and X-wind driven outflow dynamical models are tested to fit the observed morphology and kinematics of H 2.



October 2002


PHOTOMETRY OF FOURTEEN MAIN BELT ASTEROIDS

R. Gil-Hutton

Observatorio Astronómico Félix Aguilar, San Juan, Argentina.

and

M. Cañada

Depto. de Geofísica y Astronomía, Universidad Nacional de San Juan, Argentina.

rgilhutton@casleo.gov.ar

Received: 2002 October 30

Abstract: The results of CCD photometry of 14 main belt asteroids obtained between 1996 and 2000 are presented. For most of them, the V and R composite lightcurves and the values of the synodic rotational period are derived. There exists no previous determination of the period for 10 of the observed objects.


THE EFFECT OF CLOUD EVAPORATION ON THE STELLAR INITIAL MASS FUNCTION

N. Sánchez 1,2

and

J. García 1

1Departamento de Física, Facultad Experimental de Ciencias Universidad del Zulia, Maracaibo, Venezuela.

2Centro de Astrofísica Teórica, Facultad de Ciencias Universidad de Los Andes, Mérida, Venezuela.

jgarcia@orion.ciens.luz.ve

Received: 2002 October 14

Abstract: There is some observational evidence that the stellar initial mass function (IMF) flattens below 1 M, but it is still controversial whether this flattening stays constant or turns over at the low mass end. We treat this subject analyzing how the thermal evaporation of star forming clouds embedded in a warm medium can affect the shape of the IMF. An initial distribution of clouds is considered, in which each cloud is accreting mass to a central protostar. When protostellar outflows are sufficiently energetic, it is assumed that one star is formed. The formation of some stars increases the UV radiation field, heating the warm gas and increasing the evaporation rate of other clouds. It is showed that if the evaporation rate is high enough, IMFs with a turnover at low masses can be obtained. For the assumed range of parameter values, the mass of the turnover ranges from 0.2 M to 4 M. The results indicate that the IMF turnover should be shifted to higher mass values in regions of high star density, warm gas temperature and/or UV interstellar radiation field.


ON THE EXISTENCE OF DWARF SPIRAL GALAXIES

A. M. Hidalgo-Gámez

ESFC-Instituto Politécnico Nacional, México, D. F.

anamaria@astroscu.unam.mx

Received: 2002 October 9

Abstract: The investigation presented here was focused on clarify the existence of dwarf spiral galaxies as a separate group from classical spirals. First, a list of spiral galaxies with small sizes was obtained. Information on colors, luminosities, morphologies, and chemical content were searched in the literature for these galaxies. Using this information it can be concluded that dwarf spirals are not the tail of the distribution of classical galaxies. On the contrary, important differences in some of the most characteristic properties of spiral galaxies, as the metallicity gradient and the bars frecuency, were found. In any case, more and accurated observations are needed for a definitive answer.



September 2002


RELATION BETWEEN SOURCE AND TEMPERATURE FLUCTUATIONS IN PHOTOIONIZED NEBULAE

L. Binette, 1 P. Ferruit, 2 W. Steffen, 1

and

A. C. Raga 3

1 Instituto de Astronomí, Universidad Nacional Autónoma de México, México, D. F.

2 CRAL - Observatoire de Lyon, France.

3 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, México, D. F.

binette@astroscu.unam.mx

Received: 2002 September 26

Abstract: The magnitude of the temperature fluctuations ( t2) required to explain the observed inconsistencies between metallicities inferred from recombination lines and from forbidden lines cannot be attained by steady-state equilibrium photoionization models. If on the other hand the nebular ionizing source was variable, the temperature fluctuations t2 would be significantly larger. We investigate the time-dependent response of the nebular ionization and temperature structure when photoionized by a periodically varying source. We study how the asymptotic mean value, t2, behaves as a function of the period or amplitude of the source variability. We conclude that the amplitude of the exciting star variations required to achieve a t2 = 0.025 (as in the Orion nebula) is unacceptably large. Source variability is therefore not a viable mechanism to explain the observed values of t2. We reach a similar conclusion from studies of the temporal variability resulting from intermittent shadows behind opaque condensations. We find that photoionized nebulae are on average less massive but somewhat hotter in the case of cyclicly variable ionizing sources.


ESTIMATING THE PREVALENCE OF RECENT MERGERS FROM BULGE TO DISK RATIOS OF LATE TYPE GALAXIES

Xavier Hernández

Instituto de Astronomía Universidad Nacional Autónoma de México, México, D. F.

xavier@astroscu.unam.mx

Received: 2002 September 3

Abstract: We study a mechanism for the formation of bulges as a result of the gravitational dominance of the disk material over the dark halo, in the centers of disk galaxies. This provides an estimate of the bulge to disk ratio (B/D) as a function of the asymptotic rotation velocity, and the disk exponential scale length, for galaxies assembled at high redshift. Galaxies having formed through a more gradual mass aggregation history extending to low redshifts, such as is predicted by hierarchical models of structure formation, will not follow the B/D trends predicted by our model. The repeated mergings experienced by galaxies in the CDM scenario, which extend into the low redshift regime, would produce an enhancement of the B/D ratios of galaxies above the trend predicted for high formation redshift systems. We perform a comparison of the model against a recent large survey of galaxies (Moriondo et al. 1999, 2001) for which luminosity profile decompositions are available in the infrared. We find a substantial fraction which falls along the trend predicted by the models, signaling a joint formation of their bulges and disks, of the type expected in “monolithic” scenarios and giving rise to the observed correlations between disk and bulge structural parameters (e.g. Courteau et al. 1996, de Jong 1996). A significant fraction shows larger B/D ratios, signaling the effects of recent mergers of the type expected in hierarchical formation scenarios and presumably giving rise to the large spread observed in the above mentioned relations. An analysis of the relative numbers of galaxies following the high formation B/D prediction and those having enhanced B/D values can be used in principle to constrain galactic formation scenarios.



August 2002



July 2002


THE OPTICAL AND NEAR-INFRARED COUNTERPART OF IRAS 18476+20541

S. Kimeswenger, C. Lederle, and B. Armsdorfer

Institut für Astrophysik, Innsbruck, Austria

and

J. Pritchard

European Southern Observatory, ESO, Chile

Stefan.Kimeswenger@uibk.ac.at

Received: 2002 July 23

Abstract: We present here for the first time an optical and near-infrared (NIR) identification for the up to now unstudied IRAS PSC source 18476+2054. Direct imaging in BVRI CiJK s and optical spectroscopy were obtained. The optical counterpart is identified as a variable star of Mira class --M7 or later giant or supergiant-- with a mid infrared excess compared to ”normal” Miras having such a short period. The (V-I C) is remarkably high, although the (B-V) gives no indication for circumstellar extinction driving a reddening. The V-[12] color show a mid infrared excess. The photometries obtained here and the sky survey plates allow us to estimate a period of 145 days and a, for the very late spectroscopy type, unusual low amplitude of ΔV = 2.5m ± 0.2m.


GALAXIES FORMATION SIMULATIONS WITH SCALAR FIELD DARK MATTER HALOS

Tonatiuh Matos and Gabino Torres

Centro de Investigacion y de Estudios Avanzados del IPN Departamento de Física

tmatos@fis.cinvestav.mx

Received: 2002 July 23

Abstract: We present some simulations for galaxies formation using a scalar field cosmological model in which the dark matter is modeled by scalar field Φ. In the Scalar Field Dark Matter (SFDM) model the dark matter consists of an ultra-light particle, with mass mΦ 1023 eV . Since in the SFDM model all the success of the standard cold dark matter model are recovered, this suggest that the scalar field could be a good candidate to be the dark matter of the galaxies halos. In this work we perform simulations for the formation of the luminous part of galaxies using the SFDM model, supposing that a dark matter fluctuation forms and evolves attracting the luminous matter around it. Under these conditions we find that the luminous matter evolves and forms objects with spiral arms and later evolves into an object with circular symmetry, looking very similar as the observed spiral galaies.

PACS numbers: 98.80.-, 95.35.+d


EXPONENTIALLY-FITTED AND TRIGONOMETRICALLY-FITTED METHODS FOR THE NUMERICAL INTEGRATION OF ORBITAL PROBLEMS

T. E. Simos

Section of Mathematics, Department of Civil Engineering Democritus University of Thrace, Greece

tsimos@mail.ariadne-t.gr

Received: 2002 July 23

Abstract: An explicit hybrid symmetric eight-step method of algebraic order eight is presented in this paper. Numerical results from the application to well known periodic orbital problems show the efficiency of the new developed method.



June 2002


A NEW METHOD TO FIND THE POTENTIAL CENTER OF N-BODY SYSTEMS

Fidel Cruz P. and Luis A. Aguilar

Instituto de Astronomía, Unidad Ensenada Universidad Nacional Autónoma de México

and

Daniel D. Carpintero

Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentina

aguilar@astrosen.unam.mx

Received: 2002 June 24

Abstract: We present a new and fast method to find the potential center of an N-body distribution. The method uses an iterative algorithm which exploits the fact that the gradient of the potential is null at its center: It uses a smoothing radius to avoid getting trapped in secondary minima. We have tested this method on several random realizations of King models (in which the numerical computation of the potential center is rather difficult, due to their relative constant density within their cores), and compared its performance and accuracy against a more straightforward, but computer intensive method, based in cartesian meshes of increasing spatial resolution. In all cases both methods converged to the same center, within the mesh resolution, but the iterative method is two orders of magnitude faster.

We have also tested the method with one astronomical problem: the evolution of a 105 particle King model orbiting around a fixed potential that represents our Galaxy. We used a spherical harmonics expansion N-body code, in which the potential center determination is crucial for the correct force computation. We compared this simulation with another one in which a method previously used to determine the expansion center is employed (White 1983). Our routine gives better results in energy conservation and mass loss.


A REVISED CALIBRATION OF THE MV W(OI7774) RELATIONSHIP USING HIPPARCOS DATA: ITS APPLICATION TO CEPHEIDS AND EVOLVED STARS2

A. Arellano Ferro, 1 Sunetra Giridhar, 2 and E. Rojo Arellano 2

1Instituto de Astronomía, Universidad Nacional Autónoma de México. México D. F., México.

2Indian Institute of Astrophysics, Bangalore 500034, India.

armando@astroscu.unam.mx

Received: 2002 June 17

Abstract: A new calibration of the MV W(OI7774) relationship has been calculated using better estimates of reddenings and distances to a sample of 27 calibrator stars of A-G spectral types, based on accurate parallaxes and proper motions from the Hipparcos and Tycho catalogues. The present calibration predicts absolute magnitude with accuracies of ± 0.41 mag for a sample covering a large range of MV , from 9.5 to +0.35 mag. The colour term included in a previous paper has been dropped since its inclusion was not bringing any significant improvement to the calibration. The variation of the OI7774 feature in the classical cepheid SS Sct has been studied. We calculated a phase-dependent correction to random phase OI feature strengths in a Cepheids, such that it predicts mean absolute magnitudes through the above calibration. After applying such correction, we could increase the list of calibrators to 58 by adding MV and OI 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 OI7774 feature. We use our derived calibrations to estimate MV for a set of evolved objects to be able to locate their positions in the H-R diagram.


ADDITIONAL ATMOSPHERIC OPACITY MEASUREMENTS AT MILLIMETRIC WAVELENGTHS FROM SAN PEDRO MARTIR SIERRA IN BAJA CALIFORNIA

David Hiriart

Instituto de Astronomía, UNAM, Campus Ensenada, B. C., México

hiriart@astrosen.unam.mx

Received: 2002 June 17

Abstract: Measurements of the atmospheric opacity in the zenith direction for a wavelength of 1.4 mm (210 GHz) at the Observatorio Astronomico Nacional in the Sierra San Pedro Martir, Baja California, Mexico are presented. The data cover 251 days in 1999. Measurements were made in a continuous basis every eight minutes using a heterodyne radiometer. For this period, the total mean opacity at the zenith was 0.13 nepers; values of total mean opacity for night time and day time of 0.14 and 0.12 nepers respectively were found. The data presented supplement those in an earlier paper covering 210 days in 1992 (Hiriart et al. 1992). At that year a total mean sky opacity of 0.24 nepers at a frequency of 215 GHz was found. The present results confirm that measurements in 1992 were affected by El Niño activity. By comparing the results of 1999 with similar measurements made at Kitt Peak and Mount Graham observatories in the same year, it is found that the North American monsoon that increases the sky opacity at millimeter wavelength lasted two months less in Baja than in southwestern USA.


LA GRANJA: A BEOWULF TYPE COMPUTER FOR NUMERICAL SIMULATIONS IN STELLAR AND GALACTIC DYNAMICS

Héctor Velázquez and Luis A. Aguilar

Instituto de Astronomía, Unidad Ensenada Universidad Nacional Autónoma de México

aguilar@astrosen.unam.mx

Received: 2002 June 17

Abstract: We present a Beowulf type computer built using off-the-shelf hardware and freely available software. Its performance in raw computational power and parallel efficiency is compared with an SGI Origin-2000 computer using two different N-body codes. The impact of this technology, in opening up the possibility of making routine N 106 particle simulations with a computer “built at home”, is discussed. The effect of higher numerical resolution is shown with simulations of a cold dissipationless collapse and of the vertical heating of the disk component of a spiral galaxy evolved in isolation.


THE EFFECTIVE TEMPERATURE AND THE ABSOLUTE MAGNITUDE OF THE STARS

Ángel Fierros Palacios

Instituto de Investigaciones Eléctricas Temixco, Morelos, México

afierros@iee.org.mx

Received: 2002 June 12

Abstract: The theoretical framework developed by A. S. Eddington for the study of the inner structure and stability of the stars, has been modified by the author and used in this work to show that knowing the effective temperature and the absolute magnitude, the basic parameters of any gaseous star can be calculated.


THE RADIAL VELOCITY PROFILES OF SOME PROPLYDS IN THE ORION NEBULA

Eduardo de la Fuente 3, Margarita Rosado, Lorena Arias, and Patricia Ambrocio-Cruz

Instituto de Astronomía Universidad Nacional Autónoma de México

3Facultad de Ciencias, UNAM.

edfuente;margarit@astroscu.unam.mx

Received: 2002 June 12

Abstract: Radial velocity profiles of 16 protoplanetary disks in the Orion Nebula are presented. These profiles were obtained by means of H α Fabry-Perot interferometry carried out on this nebula. We discuss the main challenge in obtaining the proplyd velocity profiles: the subtraction of the bright H II region emission of the Orion Nebula that contaminates the velocity components of the proplyd emission.

We have also found that Fabry-Perot interferometry constitutes an effective technique for the detection of proplyds. Indeed, we were able to identify several proplyds (82-336, 158-323, 158-326, 159-350, 163-317, 167-317, 170-337, 177-341 and 244-440) from the raw Fabry-Perot data cubes at H α, because they appear as conspicuous, bright, point-like nebulosities. Several other proplyds (161-314, 161-324, 166-316, 168-326, 176-325, 180-331 and 197-427) were identified only after a process of “unsharp-masking”of the Fabry-Perot velocity maps. Thus, the “Fabry-Perot unsharp-masking” technique is quite powerful for the identification of proplyds from ground-based observations at optical wavelengths. The heliocentric systemic velocities were measured between 22-38 km s 1. We also present high velocity features associated to a probable HH object situated to the south of the proplyd 168-326.


A SPECTROGRAPHIC STUDY OF THE INTERACTING ECLIPSING BINARY RY SCUTI: AN EPISODE IN THE RAPID MASS LOSS STAGE OR A PROTOPLANETARY NEBULA?3

J. Sahade, 2,3,5,6 R. M. West, 3,6 and M. Y. Skul’sky 4

Sahade@fcaglp.fcaglp.unlp.edu.ar

Received: 2002 June 6

Abstract: RY Scuti, the 11-day [Fe III] eclipsing binary, has been reinvestigated on the basis of spectrographic material secured in Chile at the European Southern Observatory, La Silla, and at the Cerro Tololo Interamerican Observatory, that covers the regions of 3400-5150  and of 5700-6700 , and worked out with the measuring and computing facilities at the ESO headquarters in Garching bei München, Federal Republic of Germany. Ultraviolet IUE observations were also analyzed.

The spectrum of RY Sct is very complex and unusually peculiar, being characterized by several sets of emission as well as of absorption features. Among the emissions, there is a set of lines that are characteristic of planetary nebulae.

The system is found to be formed by a B0V component and a companion that appears to be surrounded by an opaque envelope that emits in He II  λ4686.

In the circumbinary envelope we can distinguish: a) a region of diluted radiation that suggests a velocity of 178 km s 1; b) regions of formation of the resonance lines of Si IV and C IV in the IUE UV, characterized by velocities of 1200 and 600 km s 1; c) regions that give rise to the “nebular spectrum” and suggest that there is a triple nebulosity surrounding the system with Ne probably larger than 10 4 cm 3, Te 15, 000-20,000 K and velocities of 18, +9 and +48 km s 1, respectively.



May 2002



April 2002



March 2002



February 2002


Optical Line Profile Variability of the B1+Neutron Star Binary System LS I +65 010 (2S 0114+650)

G. Koenigsberger, 1,2 G. Canalizo, 3 A. Arrieta, 1 M. G. Richer, 1 and L. Georgiev 1

1Instituto de Astronomía, Universidad Nacional Autónoma de México, México D. F.

2Centro de Ciencias Físicas, Universidad Nacional Autónoma de México, México D. F.

3Institute of Geophysics and Planetary Sciences, Livermore, USA.

gloria@astroscu.unam.mx

Received: 2002 February 26

Accepted: 2002 October 22 (RevMexAA Vol. 39 no. 1, April 2003)

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 V helio 31 ± 5 km s1, 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 V helio 70, 48 km s1, possibly associated with gas surrounding the binary system, in addition to the 24 and 8 km s1 ISM features due to the Orion and Perseus arm regions. Strong photospheric line profile variability is present on a night-to-night timescale, with He i 5875  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 profiles are detected on only two nights, but the evidence that these variations occur on the 2.78 hour X-ray flaring period is marginal.



January 2002


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