RevMexAA: Abstracts of Accepted Papers for Volume 47 Number 2

July 1, 2011

2011: July June May April March

July 2011

Missing Seyfert Galaxies

Hrant M. Tovmassian1 and O. Yam2

1Instituto Nacional de Astrofísica, Óptica y Electrónica, Puebla, Mexico
2Depto. de Ciencias, Universidad de Quintana Roo, Mexico

Received: 2011 May 11
Accepted: 2011 July 1

Abstract: The aim of this work is estimating the number of Seyfert nuclei missing in catalogs due to obscuration by the dust disc in host spiral galaxies. We compared the distribution of inclinations of host galaxies of Sy1s and Sy2s with that of in control sample of spiral galaxies, and found that the relative number of Seyferts is higher in almost face-on galaxies with i < 30 and smaller in highly inclined galaxies with i > 61 than in spiral galaxies without active nuclei. We conclude that the difference found is due to absorption of the Seyfert nuclei by the dust-disc of inclined galaxies. We estimate that about 100% and 50% of the observed Sy1s and Sy2s respectively are missing.

June 2011

Space reddenings for fifteen Galactic Cepheids

D. G. Turner,1 R. F. MacLellan,2 A. A. Henden,3 and L. N. Berdnikov4

1Saint Mary's University, Halifax, Nova Scotia, Canada
2Queen's University, Kingston, Ontario, Canada
3AAVSO, Cambridge, Massachusetts, USA
4Sternberg Astronomical Institute, Moscow, Russia

Received: 2011 February 24
Accepted: 2011 June 27

Abstract: Space reddenings are derived for 15 Galactic Cepheids from dereddening CCD BV(RI)C data for AF-type stars in the immediate vicinities of the variables, in conjunction with 2MASS reddenings for BAF-type stars in the same fields. Potential reddening solutions were analyzed using the variable-extinction method to identify stars sharing potentially similar distances and reddenings to the Cepheids, several of which have large color excesses. The intrinsic BV(RI)C color relation for AF dwarfs was modified slightly in the analysis in order to describe better the colors observed for unreddened stars in the samples.

The Proper Motion of the Large Magellanic Cloud Revisited

M. H. Pedreros1

1Departamento de Física, Facultad de Ciencias, Universidad de Tarapacá, Arica, Chile

Received: 2011 March 2
Accepted: 2011 June 24

Abstract: The proper motion (p.m.) of the Large Magellanic Cloud (LMC) relative to four background quasi-stellar objects has been determined by reading and re-processing image data from two previous studies. The total center of mass p.m. for the LMC obtained here is μ = (+1.94 ± 0.08) mas yr -1, with a position angle of θ = (61.5 ± 3.2). The new results agree reasonably well with those obtained previously by our group and by other groups and with several existing theoretical models. From the radial velocity of the center of the LMC found in the literature, in combination with the transverse velocity vector determined from the p.m. measured in the present work, we obtain the space velocity of the LMC center. Using the latter and assuming a point-mass potential for the Galaxy, we have estimated the amount of mass contained within 50 kpc of the center of the Galaxy.

The cometary cavity created by an aligned streaming environment/collimated outflow interaction

D. López-Cámara,1 A. Esquivel,1 J. Cantó,2 A. C. Raga,1 P. F. Velázquez,1 and A. Rodríguez-González1

1Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, D.F., Mexico
2Instituto de Astronomía, Universidad Nacional Autónoma de México, D.F., Mexico

Received: 2011 May 20
Accepted: 2011 June 16

Abstract: We present a "thin shell" model of the interaction of a biconical outflow and a streaming environment (aligned with the direction of the flow), as well as numerical (axisymmetric) simulations of such an interaction. A similar situation, although in a more complex setup, takes place at the head of the cometary structure of Mira. Thus, for most of the numerical simulations we explore parameters consistent with the observed bipolar outflow from Mira B. For these parameters, the interaction is non-radiative, so that a rather broad jet/streaming environment interaction region is formed. In spite of this, a reasonable agreement between the thin-shell analytic model and the numerical simulations is obtained.

uvbyβ photoelectric photometry of the open clusters NGC 6811 and NGC 6830

J. H. Peña,1 L. Fox Machado,2 H. García,3 A. Rentería,1 S. Skinner,1,4 A. Espinosa,1 and E. Romero1

1Instituto de Astronomía, Universidad Nacional Autónoma de México, D.F., Mexico
2Observatorio Astronómico Nacional, Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, Mexico
3Observatorio Astronómico, Universidad Nacional Autónoma de Nicaragua, Managua, Nicaragua
4Univerdad Nacional de Panamá, Panama

Received: 2010 October 27
Accepted: 2011 June 15

Abstract: From uvbyβ photometry of the open clusters NGC 6811 (75 stars), and NGC 6830 (19 stars) we were able to determine membership of the stars to each cluster, and fix the age and reddening for each. Since several short period stars have recently been found, we have carried out a study of these variables.

V1898 Cygni: An interacting eclipsing binary in the vicinity of North America nebula

A. Dervişoǧlu,1 Ö Çakirli,1,2 C. İbanoǧlu,1 and E. Sipahi1

1Ege University, Science Faculty, Department of Astronomy and Space Sciences, İzmir, Turkey
2TÜBİTAK National Observatory, Akdeniz University Campus, Turkey

Received: 2011 April 12
Accepted: 2011 June 12

Abstract: We present spectroscopic observations of the double-lined Algol type eclipsing binary V1898 Cyg. Analyses of the BV light curves and RVs led to determination of the fundamental stellar parameters of the V1898 Cyg's components. The absolute parameters for the stars are derived as: M1 = 6.054 ± 0.037 M, M2 = 1.162 ± 0.011 M, R1 = 3.526 ± 0.009 R, R2 = 2.640 ± 0.010 R, Teff1 = 18000 ± 600 K, and Teff2 = 6200 ± 200 K. The residuals between the observed and computed times of mid-eclipses were analysed and a rate of the period change ∕P = 6.68 × 10-7 yr -1 was obtained and a mass transfer rate of 1.88 × 10-7 M in a year is estimated. We have calculated the distance to the system of V1898 Cyg as 501 ± 5 pc using the infrared JHK magnitudes and bolometric corrections for the primary star. The components of the system’s proper motions present some indications about membership of the North America nebula.

An intepretive ballistic model for quasi-symmetric bipolar jet systems

A. C. Raga,1 A. Noriega-Crespo,2 J. C. Rodríguez-Ramírez,1 V. Lora,3 K. R. Stapelfeldt,4 and S. J. Carey2

1Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico
2Spitzer Science Center, California Institute of Technology, USA
3Astronomisches Rechen-Institut Zentrum für Astronomie der Universität Heidelberg, Germany
4Jet propulsion Laboratory, California Institute of Technology, USA

Received: 2011 April 10
Accepted: 2011 June 6

Abstract: We present an analytic, ballistic model for quasi-symmetric jet/counterjet systems, considering both the non-relativistic and the relativistic cases. The model considers the presence of ejection time and velocity asymmetries, which produce offsets between the positions of the knots in jet/counterjet pairs. A fit of the non-relativistic model predictions to observations of two quasi-symmetric HH outflows (HH 34 and HH 111) allows us to obtain the magnitudes of the ejection time and velocity asymmetries of these systems.

May 2011

Variable jets with non-top hat ejection cross sections: a model for the knots of the HH 34 jet

A. C. Raga,1 A. Noriega-Crespo,2 P. Kajdic,3 F. De Colle,4 D. López-Cámara,1 and A. Esquivel1

1Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico
2Spitzer Science Center, California Institute of Technology, USA
3Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico
4Astronomy and Astrophysics Department, University of California, USA

Received: 2010 December 15
Accepted: 2011 May 9

Abstract: We compute axisymmetric, single-sinusoidal mode variable ejection models with a non-top hat ejection velocity cross section. We find that for decreasing edge-to-centre velocity ratios one obtains internal working surfaces with progressively more extended bow shock wings. These wings produce [S II] emission which partially fills in the inter-knot regions in predicted intensity maps. We then compute 3-mode models (with parameters appropriate for the HH 34 jet), and compare predicted intensity maps with archival HST images of HH 34. We find that a model with a moderate edge-to-centre velocity ratio produces knot structures with morphologies and time-variabilites with clear similarities to the observations of HH 34.

Wind structure of the Wolf-Rayet star EZ CMa=HD 50896

Aaron Flores,1 Gloria Koenigsberger,2 Octavio Cardona,3 and Lelio de la Cruz1

1Facultad de Ingeniería, Universidad Autónoma del Carmen, Campeche, Mexico
2Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Mexico
3Instituto Nacional de Astrofísica, Óptica y Electrónica, Puebla, Mexico

Received: 2011 March 22
Accepted: 2011 May 9

Abstract: The Wolf-Rayet star HD 50896 (EZ CMa=WR6) is well-known for the emission-line profile variability that occurs on a 3.7-day timescale. In particular, the shape of the N V 4604-21 doublet changes from a P Cygni profile to one in which no blue-shifted absorption component is present. In this paper we use spectroscopic observations obtained in 1991, 1999, 2005 and 2009 to glean physical conditions within the stellar wind that may give rise to these changes. We find that variations in the opacity at a distance Rmax~0.30.5 of the stellar surface can produce the observed effects. Here, Rmax is the extent of the N V line-forming region. The results are consistent either with a scenario in which the opacity of the inner wind region of HD 50896 undergoes cyclical variations over the 3.76 d period or with a quadrupolar wind distribution in which the sectors having different opacities rotate in and out of our line-of-sight on this periodic timescale.

April 2011

Spectral morphology and rotation in open cluster NGC 6025

Mónica Grosso1,2,3 and Hugo Levato1,2,3

1Instituto de Ciencias Astronómicas, de la Tierra y del Espacio, Argentina
2Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina
3Universidad Nacional de San Juan, Argentina

Received: 2011 January 19
Accepted: 2011 April 19

Abstract: We have performed spectral classification and measurements of the axial rotation velocity for the brightest stars in the region of the open cluster NGC 6025. A distant modulus of 9.80 ± 0.06 (pe) and an age of 84 million years were derived. The brightest star of the cluster, HD 143448 was classified as B1Ve and it is a blue straggler as was proposed by other authors (see Mermilliod 1982). We have found three peculiar stars (two Si and one Hg-Mn?). Another star in the field has emission but is probably a non member. We have also found two SB2 binaries The average axial rotation for the cluster members seems to be 73% of the average rotation of the field stars with the same temperature.

On the stellar and baryonic mass fractions of central blue and red galaxies

A. Rodríguez-Puebla,1 V. Avila-Reese,1 C. Firmani,1,2 and P. Colín3

1Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico
2Osservatorio Astronomico di Brera, Italy
3Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Mexico

Received: 2011 January 21
Accepted: 2011 April 14

Abstract: Using the abundance matching technique, we infer the local stellar and baryonic mass-halo mass (Ms - Mh and Mb - Mh) relations separately for central blue and red galaxies (BGs and RGs). The observational inputs are the SDSS central BG and RG Stellar Mass Functions and the measured gas mass-Ms relations. For halos associated to central BGs, the distinct ΛCDM Halo Mass Function is used and set up to exclude: (i) the observed group/cluster mass function and (ii) halos with a central major merger at resdshifts z 0.8. For central RGs, the complement of this mass function to the total one is used. At Mh > 1011.5 M, the Ms of RGs tend to be higher than those of BGs for a given Mh, the difference not being larger than 1.7. At Mh < 1011.5 M, this trend is inverted. For BGs (RGs): (a) the maximum value of fs = Ms / Mh is 0.021+0.016–0.009 (0.034+0.026–0.015) and it is attained at log(Mh/ M)=12.0 (=11.9); (b) fsMh (fsMh3) at the low-mass end while at the high-mass end, fsMh–0.4 (fsMh–0.6). The baryon mass fractions, fb=Mb / Mh, of BGs and RGs reach maximum values of fb=0.028+0.018–0.011 and fb=0.034+0.025–0.014, respectively. At Mh < 1011.3 M, the dependence of fb on Mh is much steeper for RGs than for BGs. We discuss on the differences found in the fs- Mh and fb- Mh relations between BGs and RGs in the light of semi-empirical galaxy evolution inferences.

Upper Main Sequence Stars with Anomaluos Abundances. The HgMn stars HR 3273, HR 8118, HR 8567 and HR 8937

C. Saffe, N. Nuñez, and H. Levato

Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (ICATE), San Juan, Argentina
Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de San Juan, Argentina

Received: 2010 December 13
Accepted: 2011 April 8

Abstract: This work is part of our current study for verifying a possible relation between abundances of HgMn stars with stellar parameters, rotation and age. We present an analysis of the stars HR 3273, HR 8118, HR 8567 and HR 8937. We used echelle spectra taken with the CASLEO 2.1 m telescope and ATLAS9 model atmospheres. He I was underabundant for the HgMn stars. O was slightly underabundant in HR 3273 and HR 8567. Mg II was underabundant except for HR 8118. Si II was close to solar in HR 8118 and HR 8937, and underabundant in HR 3273 and HR 8567. Fe was slightly underabundant in HR 3273 and HR 8567, and slightly overabundant in HR 8118 and HR 8937. The species Sc, Ti, Cr, Mn, Sr, Y and Zr were overabundant while Ni was underabundant.

Speckle Interferometry at the Observatorio Astronómico Nacional. III.

V. G. Orlov, V. V. Voitsekhovich, C. A. Guerrero, F. Angeles, A. Farah Simon, E. Luna, and R. Vazquez Robledo

Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico

Received: 2011 March 10
Accepted: 2011 April 6

Abstract: We present speckle interferometric measurements of binary stars performed during August of 2010 with the 1.5 m telescope and during November of 2010 with the 2.1 m telescope of the Observatorio Astronómico Nacional at SPM (Mexico). We report here the results of 238 measurements of 225 pairs with a primary limiting magnitude of V = 12.2; 211 of them have separations less than 1”. The mean error in separation is 0.”03 and 1.5 in position angle. Some of the position angles were determined with the usual 180 ambiguity.

March 2011

The Kinematics and Velocity Ellipsoid of the G III Stars

Richard L. Branham, Jr.

Instituto Argentino de Nivologa, Glaciologa y Ciencias Ambientales, Mendoza, Argentina

Received: 2010 October 27
Accepted: 2011 March 10

Abstract: To study the kinematics of the G giant stars (luminosity class III) use is made of proper motions and parallaxes taken from van Leeuwens new reduction of the Hipparcos catalog. 3,075 stars, of which 658 have radial velocities, were used in the nal study. The solution gives: solar velocity of 16.72 ± 0.41 km s1; Oorts constants, in units of km s1 kpc1, A = 14.05 ± 3.28 and B = 9.30 ± 2.87, implying a rotational velocity of 198.48 ± 26.95 km s1 if we take the distance to the Galactic center as 8.2 ± 1.1 kpc; velocity dispersions, in units of km s1, of σx = 51.78 ± 0.55, σy = 42.81 ± 0.32, σz = 28.45 ± 0.22 with a vertex deviation of 3.88 ± 6.62. A comparison of the velocity dispersions with those given by other spectral types shows that Parenagos discontinuity also exists for the giant stars.