VARIABILITY AND STAR FORMATION IN LEO T, THE LOWEST LUMINOSITY STAR-FORMING GALAXY KNOWN TODAY

被引：50
|
作者：
Clementini, Gisella [1 ]
Cignoni, Michele [1 ,2 ]
Ramos, Rodrigo Contreras [1 ,2 ]
Federici, Luciana [1 ]
Ripepi, Vincenzo [3 ]
Marconi, Marcella [3 ]
Tosi, Monica [1 ]
Musella, Ilaria [3 ]
机构：
[1] Osservatorio Astron Bologna, INAF, I-40127 Bologna, Italy
[2] Univ Bologna, Dipartmento Astron, I-40127 Bologna, Italy
[3] Osserv Astron Capodimonte, INAF, I-80131 Naples, Italy
来源：
ASTROPHYSICAL JOURNAL | 2012年 / 756卷 / 02期
关键词：
galaxies: dwarf; galaxies: individual (Leo T); galaxies: stellar content; stars: formation; stars: variables: Cepheids; stars: variables: RR Lyrae; RR-LYRAE STARS; DWARF SPHEROIDAL GALAXY; SURFACE BRIGHTNESS PROFILES; SMALL-MAGELLANIC-CLOUD; METAL-POOR VARIABLES; MILKY-WAY SATELLITES; POPULATION-II STARS; URSA-MAJOR II; GLOBULAR-CLUSTERS; FORMATION HISTORY;
D O I：
10.1088/0004-637X/756/2/108
中图分类号：
P1 [天文学];
学科分类号：
0704 ;
摘要：
We present results from the first combined study of variable stars and star formation history (SFH) of the Milky Way "ultra-faint" dwarf (UFD) galaxy Leo T, based on F606W and F814W multi-epoch archive observations obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We have detected 14 variable stars in the galaxy. They include one fundamental-mode RR Lyrae star and 11 Anomalous Cepheids with periods shorter than 1 day, thus suggesting the occurrence of multiple star formation episodes in this UFD, of which one about 10 Gyr ago produced the RR Lyrae star. A new estimate of the distance to Leo T of 409(-27)(+29) kpc (distance modulus of 23.06 +/- 0.15 mag) was derived from the galaxy's RR Lyrae star. Our V, V - I color-magnitude diagram (CMD) of Leo T reaches V similar to 29 mag and shows features typical of a galaxy in transition between dwarf irregular and dwarf spheroidal types. A quantitative analysis of the SFH, based on the comparison of the observed V, V - I CMD with the expected distribution of stars for different evolutionary scenarios, confirms that Leo T has a complex SFH dominated by two enhanced periods about 1.5 and 9 Gyr ago, respectively. The distribution of stars and gas shows that the galaxy has a fairly asymmetric structure.
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页数：16
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