RevMexAA: Abstracts of Accepted Papers for Volume 47 Number 2

April 25, 2011

2011: a href="#May:2011">May April March

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 \msun$, this trend is inverted. For BGs (RGs): (a) the maximum value of $f_{\rm s}=M_{\rm s}/M_{\rm h}$ is 0.021+0.016-0.009 ($0.034^{+0.026}_{-0.015}$) and it is attained at $\log(M_{\rm h}/\msun)$=12.0$ (=11.9); (b) $f_{\rm s}\propto$ $M_{\rm h}$ ($f_{\rm s}\propto M_{\rm h}^3$) at the low-mass end while at the high-mass end, $f_{\rm s}\propto M_{\rm h}^{-0.4}$ ($f_{\rm s}\propto M_{\rm h}^{-0.6}$). The baryon mass fractions, $f_{\rm b}=M_{\rm b}/M_{\rm h}$, of BGs and RGs reach maximum values of $f_{\rm b}=0.028^{+0.018}_{-0.011}$ and $f_{\rm b}=0.034^{+0.025}_{-0.014}$, respectively. At $M_{\rm h}<10^{11.3} \msun$, the dependence of $f_{\rm b}$ on $M_{\rm h}$ is much steeper for RGs than for BGs. We discuss on the differences found in the $f_{\rm s}$-$M_{\rm h}$ and $f_{\rm b}$-$M_{\rm h}$ 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 Aut&ocaute;noma 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 s-1; Oorts constants, in units of km s-1 kpc-1, A = 14.05 ± 3.28 and B = -9.30 ± 2.87, implying a rotational velocity of 198.48 ± 26.95 km s-1 if we take the distance to the Galactic center as 8.2 ± 1.1 kpc; velocity dispersions, in units of km s-1, 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.