Determinación de abundancias fotométricas y selección de miembros físicos de alta luminosidad en 11 cúmulos abiertos

Se analizan y discuten nuevos datos fotoeléctricos de alta precisión de estrellas G y K de los siguientes cúmulos: NGC 2232, NGC 2264, NGC 2335, NGC 2343, Ruprecht 10, NGC 2451, Ruprecht 46, NGC 2527, NGC 2546, NGC 2548 y NGC 2567. La discriminación entre posibles miembros físicos y estrellas del campo galáctico se llevó a cabo usando dos criterios fotométricos independientes. Contrariamente a lo sugerido por algunos autores, se encuentra que los cúmulos jóvenes NGC 2232, NGC 2264 y NGC 2451 muy probablemente no poseen gigantes rojas. Usando métodos apropiados y recientes calibraciones del sistema DDO, se determinaron excesos de color, distancias, abundancia de elementos pesados, temperaturas efectivas, gravedades superficiales y masas de las gigantes rojas. Se presentan nuevas evidencias observacionales del efecto de pérdida de masa en la mayoría de los cúmulos estudiados. Las abundancias determinadas fotométricamente oscilan entre [Fe/H] ≃ -0.2 en Ruprecht 46 y [Fe/H] ≃ 0.3 en NGC 2546.Asociación Argentina de Astronomí

Fotometría fotoeléctrica UBV del cúmulo abierto NGC 5460

Dadas las características poco conocidas del cúmulo galáctico austral NGC 5460, se decidió realizar un estudio fotométrico UBV y Hβ de las estrellas en la vecindad del mismo. En este informe de trabajo se presentan los resultados obtenidos a partir de la fotometría UBV solamente, puesto que las observaciones en Hβ se encuentran actualmente en proceso de reducción.Asociación Argentina de Astronomí

Fotometría fotoeléctrica UBV del cúmulo abierto NGC 5460

Dadas las características poco conocidas del cúmulo galáctico austral NGC 5460, se decidió realizar un estudio fotométrico UBV y Hβ de las estrellas en la vecindad del mismo. En este informe de trabajo se presentan los resultados obtenidos a partir de la fotometría UBV solamente, puesto que las observaciones en Hβ se encuentran actualmente en proceso de reducción.Asociación Argentina de Astronomí

Chemical properties of red giants belonging to the plane and the galactic disk

The distribution of heavy elements in the plane and the disk of our own Galaxy is examined from new UBV, DDO, and CMT₁T₂ photometric data of red giants belonging to fifiy open clusters. The metal content is derived from the following four abundances parameters: δ(U-B), δCN, Δ(C-M), and Δ(M-T₁), which take information not only from the blue-ultraviolet spectral region but also from the near red. It is found that: (1) In general, the δ(U-B) and δCN parameters give results very close to those of the Fe+CNO-sensitive Δ(C-M) index of the Washington system. (2) CNO is enhanced with respect to the iron-peak elements in the giant branches of some clusters. (3) Regardless the morphology, age and position in the Galaxy, all the red evolved stars in the same cluster are, in general, identical in chemical composition. This result holds for the clusters having enhancement of the CNO elements. Arguments are presented which allow us to reject the convection as a mixing mechanism of heavy elements to the surface of the stars from interiors. Although no evidence for a variation of [Fe/H] with age in the last 6x10⁸ years is found, this stellar population appears to be, in the mea, neighborhood K giants. These clusters may probably have formed from material which was not sufficiently well mixed during the last ∼6x10⁸ years. On the other hand, although the disk clusters show a clear variation of abundance with age, the metallicity of the younger disk clusters is similar, in the mean, to those of the galactic plane. The existence of an abundance gradient in the disk and the plane of our own galaxy is clearly demonstratedAsociación Argentina de Astronomí

Photometric study of the open cluster NGC 2232

Three color photoelectric photometry is presented for 43 stars in the vicinity of the southern galactic cluster NGC 2232. The stars range in V magnitude from 5.O mag to 11.4 mag. Photoelectric measurements of Hβ line intensity of 22 early-type stars is also presented. An small and uniform (B-V) color excess of 0.01 mag was found for the cluster. Independent analyses of UBV and Hβ data confirm that NGC 2232, with a minimum membership of 19 stars, is located at a distance of 360 pc. A good agreement between the absolute magnitude calibrations and intrinsic color relations derived from both UBV and Hβ photometry is confirmed. A nuclear age of 20 X 10⁶ years was obtained for the cluster.Asociación Argentina de Astronomí

Composición química en la galaxia: distribución de elementos pesados en el disco y en el plano

Observations on the UBV and DDO photometric systems have been obtained for 182 red evolved stars in 53 open clusters belonging to the disc and the galactic plane. Cluster membership was confirmed for 77 % of the stars by using two independent criteria. Interstellar reddening, ultraviolet excess, and cyanogen anomalies have been determined for the stars. The clusters were ordered by their relative ages in a self-consistent sequence. The variation of [Fe/H] with age and position in the galaxy was analysed. Although the abundance determinations for the youngest clusters are very uncertain, their [Fe/H] values appear to be higher in the mean than the average for solar neighborhood K giants. No evidence for a variation of [Fe/H] with age in the last ∼10⁹ years was found. On the other hand, a trend of decreasing metal content with increasing age seems to exist for the disc clusters. An examination of the location of the clusters in the galaxy supports the conclusion that position rather than age could be the dominant factor determining the metal abundance of stars in our galaxy.Asociación Argentina de Astronomí

Propiedades físicas de estrellas rojas evolucionadas en cúmulos abiertos

Results from photoelectric UBV and DDO photometry of post-main sequence stars in four southern open clusters are presented. Recent calibrations of DDO photometry make possible estimates of interstellar reddening, distance modulus, and a gravity-dependent index of cyanogen strength all for a single G or K evolved star. There is no evidence for mixing of heavy elements to the surface of the stars from their interiors among any of the stars observed in each cluster. This result holds for the clump stars at the blue end of the giant branch in the two older clusters observed. The apparent homogeneity of chemical properties of the clusters is interpreted as demonstrating that surface abundances of the four clusters reflect their primordial compositions.Asociación Argentina de Astronomí

Fotometría fotoeléctrica UBV del cúmulo abierto NGC 5460

Dadas las características poco conocidas del cúmulo galáctico austral NGC 5460, se decidió realizar un estudio fotométrico UBV y Hβ de las estrellas en la vecindad del mismo. En este informe de trabajo se presentan los resultados obtenidos a partir de la fotometría UBV solamente, puesto que las observaciones en Hβ se encuentran actualmente en proceso de reducción.Asociación Argentina de Astronomí

Photometric study of the open cluster NGC 2232

Three color photoelectric photometry is presented for 43 stars in the vicinity of the southern galactic cluster NGC 2232. The stars range in V magnitude from 5.O mag to 11.4 mag. Photoelectric measurements of Hβ line intensity of 22 early-type stars is also presented. An small and uniform (B-V) color excess of 0.01 mag was found for the cluster. Independent analyses of UBV and Hβ data confirm that NGC 2232, with a minimum membership of 19 stars, is located at a distance of 360 pc. A good agreement between the absolute magnitude calibrations and intrinsic color relations derived from both UBV and Hβ photometry is confirmed. A nuclear age of 20 X 10⁶ years was obtained for the cluster.Asociación Argentina de Astronomí

Photometric study of the open cluster NGC 2232

Three color photoelectric photometry is presented for 43 stars in the vicinity of the southern galactic cluster NGC 2232. The stars range in V magnitude from 5.O mag to 11.4 mag. Photoelectric measurements of Hβ line intensity of 22 early-type stars is also presented. An small and uniform (B-V) color excess of 0.01 mag was found for the cluster. Independent analyses of UBV and Hβ data confirm that NGC 2232, with a minimum membership of 19 stars, is located at a distance of 360 pc. A good agreement between the absolute magnitude calibrations and intrinsic color relations derived from both UBV and Hβ photometry is confirmed. A nuclear age of 20 X 10⁶ years was obtained for the cluster.Asociación Argentina de Astronomí