# RevMexAA: Abstracts of Recently Received Papers

### December 2001

 ANALYSIS OF SELECT RR LYRAE STARS FROM uvby-beta José H. Peña Instituto de Astronomía, Universidad Nacional Autónoma de México, D.F., México jhpena@astroscu.unam.mx Received 2001 December 4 Analysis from the $uvby-beta$ photoelectric photometry of several RR Lyrae stars in the literature is carried out. From it, the physical parameters log $T_eff$ and log g were determined as well as the metallicity. From the latter quantity, and $M_V$ determination was carried out and a distance for each star was estimated. New frequencies are proposed for two stars.

 VLA DETECTION OF THE EXCITING SOURCES OF THE MOLECULAR OUTFLOWS ASSOCIATED WITH L1448 IRS2, IRAS 05327+3404, L43, IRAS 22142+5206, L1211, AND IRAS 23545+6508 Guillem Anglada & Luis F. Rodríguez Instituto de Astrofísica de Andalucía, CSIC, Spain guillem@iaa.es Received 2001 December 4 We present sensitive VLA observations at 3.6-cm of nine fields containing molecular outflows. We detected candidates for the exciting sources of the molecular outflows in six of the fields: L1448 IRS2, IRAS~05327+3404, L43, IRAS~22142+5206, L1211, and IRAS~23545+6508. We discuss the parameters of these sources, as well as their relation with sources detected at other wavelengths.

### November 2001

 uvby -beta PHOTOMETRY OF THE RR LYRAE STAR AC AND J. H. Peña, R. Peniche, A. A. Gallegos, M. A. Hobart, & C. de la Cruz Instituto de Astronomía, Universidad Nacional Autónoma de México, México, D. F. jhpena@astroscu.unam.mx Received 2001 November 5 Stromgren uvby-beta and differential V photoelectric photometry of the variable star AC And is presented. Analysis of this data, as well as that from the literature, corroborates the periods proposed by Fitch & Szeidl (1976, hereinafter F&S). Determination of the reddening has served to determine the physical parameters log g and log T_e, as well as the metallicity [Fe/H]. The determination of M_v is discussed and, in view of it, AC And is proposed to be an RR Lyrae star.

### August 2001

 THE EXTREME TYPE I PLANETARY NEBULA M2-52 Miriam Peña and Selene Medina Instituto de Astronomía, Universidad Nacional Autónoma de México, D.F., México miriam@astroscu.unam.mx Received 2001 August 14 High-resolution spectrophotometric data of the central zone of the Br-type planetary nebula M2-52 is presented. The analysis of the spectra shows that He and N are very enhanced in M2-52. Thus, this object can be classified as an extreme Peimbert's Type I PN. The chemical composition of the ionized gas is: He/H = 0.164$\pm$0.010, O/H = (2.70$\pm$0.50)$\times$ 10$^{-4}$, N/O = 2.20$\pm$0.40, Ne/O = 0.36$\pm$0.05, and Ar/O = (6.70$\pm$1.50)$\times$10$^{-3}$. The expansion velocity of the nebula is, on average, about 20 km s$^{-1}$, but the low ionization species (N$^{++}$ and S$^{++}$) show lower expansion velocities (17 km s$^{-1}$) than O$^{++}$ and He$^+$ which have v$_{\rm exp}$ = 19 km s$^{-1}$ while H$^+$ and He$^{++}$ show v$_{\rm exp} \sim 22$ km s$^{-1}$. This behavior indicates that the outer zones of the ionized gas could have been decelarated by the molecular ring found around the central star.

### June 2001

 N-BODY SIMULATIONS OF SMALL GALAXY GROUPS H. Aceves and H. Velázquez Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, B. C., México aceves@astrosen.unam.mx Received 2001 June 13 We present a series of N-Body simulations aimed to study the dynamics of small groups of galaxies. In particular, we compare our results with the dynamical properties of Hickson's compact groups (HCG's), and study the merging history in the simulations. We consider maximum expansion' and virial initial conditions, and no primordial dark halo is considered. We find no over-merging problem, and the median properties of Hickson's groups are well reproduced by the most advanced stage of collapsing groups. Moreover, an important fraction ($\sim$ 40%) of groups initially in virial equilibrium can last for $\sim$ 10 Gyr without complete merging. The results found provide an alternative solution to the over-merging expected in Hickson's compact groups. Also, we find that the mass-to-light ratio of HCG's are probably similar to those found in clusters, suggesting that both kinds of systems have about the same fraction of baryon to total mass.

### May 2001

 V588 MON AND V589 MON, TWO DELTA SCUTI STARS IN NGC 2264 J. H. Peña, R. Peniche1,*, and F. Cervantes Instituto de Astronomía, Universidad Nacional Autónoma de México, México, D. F. jhpena@astroscu.unam.mx Received 2001 May 7 Both differential and absolute photoelectric photometry of the short period variable stars V588 Mon (W2) and V589 Mon (W20) in the direction of the Open Cluster NGC 2264 has been carried out. From $uvby-\beta$ photoelectric photometry, the physical characteristics of each star have been obtained and are presented. The differential photometry of the variables allowed us to carry out a Fourier analysis of the data. The frequencies determined for each star are: for W2, 7.1868, 10.5034, 5.7199 c/d and for W20, 6.5087, 7.1747, and 11.6703 c/d.

### April 2001

 THE EFFECT OF BINARITY AND METALLICITY IN THE SPECTRA OF WC AND WO STARS R. F. Viotti, V. F. Polcaro, L. Norci, and C. Rossi Istituto di Astrofisica Spaziale, CNR, Roma, Italy uvspace@saturn.ias.rm.cnr.it Received 2001 April 19 We study the behaviour of the intensity and width of selected emission features of an extensive sample of WC and WO stars. %have been studied as function of the spectral class. The composite spectrum (WR+OB) stars tend to have lower values of line equivalent width. Taking the median values for the single-spectrum stars emission features as reference, the OB/WR continuum ratio comes out to be as large as one dex. The equivalent width of the 581 nm C IV line in the LMC WC4 single stars is found to be on the average 2 times stronger than in galactic stars; an even larger difference is observed between galactic and non-galactic WO stars. The 465 nm blend shows a similar trend. We suggest that the observed effect on these two lines depends on the metallicity of the parent galaxy. The O V 559 nm equivalent width increases smoothly from late to early spectral types both for galactic and non-galactic objects, therefore showing to be a good temperature indicator for WO and early WC stars. A larger than expected contribution of He II to the 465 nm feature is evident in the WO/early WC stars.

### March 2001

 H2 VELOCITY STRUCTURE IN HH 211 L. Salas, I. Cruz-González and M. Rosado Instituto de Astronomía, Universidad Nacional Autónoma de México, México, D. F. salas@astrosen.unam.mx Received 2001 March 14 We describe the velocity structure of the molecular outflow HH 211 in the 2.12 $\mu$m line of H_2. Observations were obtained using an IR Fabry- Pérot interferometer with a spectral resolution of 24 km~s$^{-1}$. A comparison of the kinematics and dynamics of H_2 and the previously found for CO are discussed. The jet and X-wind driven outflow dynamical models are tested to fit the observed morphology and kinematics of H_2

### February 2001

 DISCUSSION ON THE OBLIQUITY OF THE ECLIPTIC, ECCENTRICITY OF THE EARTH'S ORBIT AND SOLAR ASTROLABE MEASUREMENTS P. C. R. Poppe, V. A. F. Martin, and N. V. Leister Observatório Astronômico Antares, UEFS, Feira de Santana-BA, Brazil poppe@.uefs.br Received 2001 February 28 In the first part of the paper, the observations of the Sun carried out with the solar astrolabe in both hemispheres will be shortly considered. A set of corrections for some parameters of the Earth's orbit will be examined. In the second part, using classical concepts of mechanics, we investigate how the obliquity of the ecliptic may be partially controlled by the eccentricity of the Earth's orbit.

### January 2001

 AN IMPROVEMENT OF THE SINGLE PL APPROXIMATION IN SPHERICAL GEOMETRY WITH A CENTRAL POINT SOURCE Vladimir Escalante Instituto de Astronomía, Universidad Nacional Autónoma de México, Campus Morelia, México v.escalante@astrosmo.unam.mx Received 2001 January 18 A new way of calculation for the single-interval spherical harmonics method in radiative transfer is proposed in which some of the last even moments are changed for odd moments. The proposed method improves significalty the accuracy and convergence of the solution in spherical inhomogeneous media with strong forward peaking of the radiation. The results compare favorably with other methods of solution for spheres with a central point source.

### October 2000

 RESPONSE OF A BALLOON-BORNE OMNIDIRECTIONAL DETECTOR TO THE ATMOSPHERIC SECONDARY CHARGED COSMIC RADIATION AT A PLACE OF 11.5 GV GEOMAGNETIC CUT-OFF I. N. Azcárate Instituto Argentino de Radioastronomía, Argentina iazcarate@yahoo.com Received 2000 October 30 An experiment performed with a belloon-borne large plastic scintillator is described. The detected system was transported by a stratospheric balloon, that was launched from Reconquista, provincia of Santa Fe, Argentina, on 24 February 1992 (geomagnetic cut-off 11.5 GV). The energy loss spectra of both atmospheric gamma-radiation (for E$_\gamma \geq 4.15$ MeV) and the charged component of the secondary cosmic radiation, were alternatively measured at different altitudes, during the ascent of the balloon and at ceiling altitude. The atmospheric gamma-ray spectrum is analyzed in an earlier paper (Azcarate 2000). The shape of the energy loss spectrum due to charged radiation can be justified, at least qualitatively, by the computation of the response of the detector to this type of radiation. It is argued that, at ceiling altitude, the observed characteristic feature in the spectrum is due mainly to relativistic muons inciding horizontally on the detector. The growth curve for the counting rate below the peak and the intensity of relativistic $\mu$ mesons were also obtained.

### August 2000

 MORPHOLOGY AND SPECTRAL BEHAVIOR OF SOLAR HARD X-RAY SOURCES Francisco C. R. Fernandes and Hanumant S. Sawant Instituto Nacional de Pesquisas Espaciais (INPE), São José dos Campos, SP, Brazil guga@das2.inpe.br Received 2000 August 23 Images of the 17 solar flares, corresponding to 61 individual X-ray bursts observed in four energy ranges (14-23, 23-33, 33-53 and 53-93 keV) by Hard X-ray Telescope (HXT) experiment on board of {\it Yohkoh} satellite have been investigated. The images suggested the dimension of hard X-ray sources is of the order of 20 arc seconds and they are of three types: single isolated source ($\sim$ 30 \%), double sources ($\sim$~41~\%), with typical minimum separation of 30 arc seconds, and multiple sources ($\sim$ 29 \%). We have adjusted single power law spectrum for the X-ray emissions, in the range of (20-830 keV), using data of Hard X-ray Spectrometer (HXS) experiment. Spectral time evolution of these bursts have been also investigated. Typical spectral index behavior is soft-hard-soft''.

### July 2000

 UBVRI AND uvby$\beta$ PHOTOMETRY OF THE GALACTIC CLUSTER HAFFNER 19 M. A. Moreno-Corral, C. Chavarría-K., and E. de Lara Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, B. C., México mam@bufadora.astrosen.unam.mx Received 2000 July 31 We present UBV(RI)_$C$ photometry of 334 stars down to V = 19$^M$ in the direction of the open cluster Haffner 19. From it, we derive spectral types of 33 of the brightest stars of the sample, confirming that they belong to a young stellar population. From their magnitudes and colors, we find a moderate and fairly homogeneous interstellar extinction in the direction of the cluster, as well as no indication of significant intercluster variable extinction. We analyze the cluster membership of the sample stars in terms of their location in the magnitude color diagrams (V, B-V), (I, R-I) and color-color (U-B, B-V) and (V-R, V-I) diagrams. Based on the photometry and on the radial velocity field of the H II region associated with Haffner 19 we discuss its distance estimates. Finally, assuming a spectral type B0V for CD--25°5205, the exciting star of the Strömgren sphere, located in the cluster's center, we derive its ionization structure.

 SMALL FIELD CCD ASTROMETRY WITH A LONG FOCUS REFLECTOR TELESCOPE I. H. Bustos Fierro and J. H. Calderón Observatorio Astronómico, Univ. Nal. de Córdoba, Rep. Argentina ivanbf@oac.uncor.edu Received 2000 July 11 It is shown a first attempt of using the block adjustment method in order to determine astrometric positions from a mosaic of CCD frames taken with a long focus reflector telescope. The observations cover an area of 25´ × 25´ around the open cluster Rup21. The source of reference positions was ACT Reference Catalog. The internal error of measured positions is analyzed, and external error is estimated from comparison with catalogs Tycho-2 and USNO-A2.0. In this comparison it is found that direct CCD images taken with focal reducer could be distorted by severe field curvature. The effect of distortion presumably introduced by the focal reducer is eliminated with suitable corrections to stellar positions measured on every frame, but a new systematic effect on scales of the entire field is observed. This effect is modeled with polynomials. Final positions have accuracy around 0.24".

### December 1999

 STUDY OF THE EXTINCTION LAW IN M31 AND SELECTION OF RED SUPERGIANTS Petko Nedialkov and Todor Veltchev Department of Astronomy, University of Sofia, Bulgaria japet@phys.uni-sofia.bg Received 1999 December 8 An average value of the total-to-selective-extinction ratio R_V = 3.8±0.4 in M31 is obtained by means of two independent methods and by use of the analytical formula of Cardelli, Clayton, & Mathis (1989). This result differs from previous determinations, as well from the standard' value 3.1 for the Milky Way. The derived individual extinctions for blue and red luminous stars from the catalogue of Magnier et al. (1992) are in good agreement with recent estimates for several OB associations in M31 and thus the issue about the assumed optical opacity of the spiral disk still remains open. The presented list of 113 red supergiant candidates in M31 with their extinctions and luminosities contains 60 new objects of this type, which are not identified in other publications. It is supplemented with further 290 stars dereddened on the base of results for their closest neighbors. The luminosity function of all red supergiant candidates and the percentage of those with progenitors over M_o suggests that the evolution of massive stars in M31 resembles that in other Local Group galaxies.

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