AGB Stars in the
External Systems

Configurations 　　　Targets　　　l-b

Research Title : AGB stars in the external systems

Abbreviation of the Research Title : AGBEXYS

PI : Nakada Yoshikazu, Univ. Tokyo, nakada@kiso.ioa.s.u-tokyo.ac.jp

Co-Is :
Tanabe Toshihiko, Univ. Tokyo, Miyata Takashi, Univ. Tokyo, Mito Hiroyuki, Univ. Tokyo, Ita Yoshifusa, Univ. Tokyo, Matsunaga Noriyuki, Univ. Tokyo, Onaka Takashi, Univ. Tokyo, Izumiura Hideyuki, NAOJ, Yanagisawa Kenshi, NAOJ, Fujii Takahiro, U. Kagoshima, Yamamura Issei, ISAS, Matsuura Mikako, UMIST, A. Zijlstra, UMIST, M. Parthasarathy, IIA, A. Kucinskas, ITPA, M.W. Feast, SAAO, J.W. Menzies. SAAO, P.A. Whitelock. SAAO, L. Leeuw, SAAO, Kyung Jeong. Meudon, H. Sung, KAO, L. Sanggak, SNU

IRC Pointing
Mode - Photometry
Band - N2, N4, S7, S9W, L15, L20W

Purpose

It is widely accepted that some AGB stars are experiencing a rapid mass loss which seriously affects their evolutionary paths. Since the spectral distribution of the mass losing stars peaks in the infrared wavelengths, Astro-F is the most suitable tool to solve some of the long-standing problems concerning the mass loss from red giant stars. Since the mass losing phase is short compared to the total life of a star, it is important to observe as many clusters as possible to achieve an enough accuracy for the statistical arguments.

1) Mass loss from AGB stars
The primary aim of this proposal is to determine the mass loss rates from AGB stars as a function of the initial mass and the metallicity. The RGB and AGB evolution including the final mass loss phase will be traced also for each set of initial mass and metallicity. The stellar clusters with homogeneous chemistry and coeval population are the best sites for this purpose: the mass loss rates will be derived from individual stars by using the infrared excess of the individual stars, while the deviation of the evolutionary paths from the non-mass-loss case will be measured on the observational color-magnitude diagram. The Large and Small Magellanic Clouds as well as the Milky Way have provided us with such clusters. However, for the quatitative analysis, we need dwarf galaxies of the Local Group, too, to cover a wider span of age and metallicity. Although these galaxies cannot be regarded as the simple stellar population, it is still rather easy to analys their stellar components. They will offer the opotunity to study the stellar populations with different background from the Magellanic clusters.

2) Star formation history revealed by the AGB stars
Many of the Local Group galaxies are dwarf spheroidals showing no star formation activities at present. However, the existence of bright AGB stars indicates that the spoladic or continuous star formation took place long after the epoch of the galaxy formation. The dwarf irregulars which are more active in the current star formation are suitable to study the more massive stars than those in the dwarf spheroidals. Generally speaking, the bigger syste has experienced the more complicated history. It is very difficult to encode the star formation history of the large galaxy like ours or M31. But still the mass losing AGB stars which are at the end of their life time reveal valuable information of the past star formation rate. With the help of the empirical relation between the luminosity and the age of the tip AGB star, it is possible to reconstruct the history of the star formation. The AGB and RGB phase transition is another interesting phenomenon which has not been studied yet in the mid-infrared wavelengths. The previous JHK study showed that the AGB transition was not so strong as the RGB one. However, the bright mass losing stars might reverse the situation in the mid-infrared. If the AGB transition is found strong in the mid-infrared, it could be used as another time indicator of the galaxies.

Method

The target will be observed by the IRC pointing mode with the total exposure time of about 10 minutes. The same filter set, N2, N4, S7, S9W, L15, L20W will be used in order to obtain the homogeneous data. Some intersting objects will additionally be observed by the grism mode. All the objects in the frames will be measured photometrically. The analysis will be performed basically by the CMD.

Uniqueness

The near- to mid-infrared wavelengths are of primary importance in the SED of the AGB stars, and the Local Group galaxies are the best sites for the evolutionary study of the AGB stars. Astro-F has the capability to combine these two advantages to understand the long entangled problem of the final evolution of low to intermediate mass stars.
The modern astronomy is now focusing on the stellar astrophysics in the external galaxies. Large ground-based telescopes will obtain the visible and near-infrared data but Astro-F data by this program will be the only source of the mid-infrared images for the Local Group galaxies.

Expected results

Homogeneous and extended sample of the infrared images will be obtained for the Galactic globular clusters and the Local Group galaxies. The color-color and the color-magnitude diagrams will be studied to search for the relation between their morphological properties and two physical parameters, age and metallicity. The AGB tip luminosity will be of main concern to see if it could be used as the age discriminator of the stellar population. The mass loss rate will be determined from the color excess in the mid-infrared and its metallicity dependence will be studied statistically.
The evolutinary models will be calculated with the mass loss rate empirically detemined by this program, This will be a crucial test for the stellar evolution model to see if it shows a reasonable fit to the observed color magnitude diagram. After we determine the evolutionary paths for AGB stars with given values of initial mass and metallicity, we will go to the application of our results to the more complicated system, M31 and M33, which are large complex system with complicated star formation history. The spatial change of the stellar population will be of particular importance to understand the evolution of these giant galaxies.

Follow-up plan
Some globular slusters in the Magellanic Clouds were monitored by us at SAAO using a near-infrared camera PANIC. The observation is extended to more clusters now and the central bars of the LMC and SMC are also monitored now by the SIRIUS camera on the IRSF at SAAO as a part of Japan and South Africa co-working program. Near-infrared monitorings of some dwarf spheroidals are also performed by the SAAO and U. Tokyo group. Southern globular clusters are surveyed now and Northern ones will be observed at Kiso Observatory this year.
We are preparing a set of special filters for the SUBARU SupCam to separate carbon stars from M stars. If the proposal is accepted, we will start the optical survey of the carbon and M-type stars for M31, M33, and other Local Group galaxies

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Configurations 　　　Targets　　　l-b

Targets

16xA+2XB+2XC+3XD+9X?+???
=64+16+16+48+9X?+???=144+9X?+???

Normal galaxies
Name 　Type 　　l　　　　　　　　b　　　　　　Position　　 Filter 　　Texp(min)
M31　　 SbI　　 27.84893 　 33.34916 　　　　　　　　　　　　　　　　　　　　　　　　　　Independently proposed.
M33 　　ScIII 　33.16433 　 19.21555 　　　 D　　　　　
M32 　　E2 　　27.6159 　　32.9954
N147 　 Sph 　 30.4666 　 40.4822 　　　　　？
N185 　 Sph 　31.4296 　　39.8436 　　　　　？
N205 　 Sph 　27.3775 　　 33.558 　　　　　？

Irregular Galaxies
Name 　Type 　　l 　　　　　　　b　　　　　　Position　　 Filter 　　Texp(min)
WLM 　 IrIV 　354.1652 　-14.35432 　　　　B
IC 10 　IrIV　　 37.0256 　　50.4234 　　　　 A
SMC 　 IrV 　 312.1375 　-64.5833 　　　　
IC1613 IrV 　　 15.7463　 -4.3968 　　　　　 C
LMC 　 IrIII 　 317.9984 -85.2487
Leo A 　IrV 　 141.1087 　17.2961 　　　　　 D
SgrDIG IrV 　　291.437 　　4.1027 　　　　　 ?
N6822　IrIV 　295.4673 　　6.3483 　　　　　 B
Aquar 　dIrV 　310.6334 　　4.9004 　　　　　?
Peg　　 IrV 　　358.8005 　16.6267 　　　　　?

Dwarf spheroidals

And III 　dSph 　23.7652　 29.7897 　　　　　A
And I 　dSph 　 26.6851 　　30.1877 　　　　 A
Scul 　 dSph 　358.3568 　-36.5111 　　　　A
Pisces　dIr 　　　23.2234 　　13.9160 　　　　A
And V 　dSph 　 36.7934 　　36.6477 　　　　A
And II 　dSph 　 30.7871 　　23.3744 　　　　A
Phoen　dIr 　　　　2.4017 　-50.7867 　　　　A
Fornax 　dSph 　22.4052 　-46.91196 　　　 D
Carina 　dSph 　113.6716 　-73.5510 　　　　?
Leo I　　 dSph　 149.7233 　　0.7892 　　　　A
Sext 　　dSph 　155.7852 　-11.8157 　　　　?
Leo II 　dSph 　 160.487 　　 15.7698 　　　　A
U Mi 　 dSph 　 158.4046 　　73.48897 　　　A
Draco 　dSph 　237.369 　　　80.22555 　　　A
Sgr 　　 dSph 　 281.9412 　　-7.607934 　　?
Tucana dSph 　309.6254 　　-50.36322 　　　A
Cas　　 dSph 　　19.5995 　　　48.2956 　　　 A
AndVI 　dSph 　　 8.4608 　　　23.26797 　　 A

Beyond the Local Group
N3109 　IrIV 　　163.8551 　　-35.36003 　　 C
Antlia 　dSph 　　164.5944　　 -36.37971 　　A
SextansB 　dIrr　
Sextans A 　dIrr
EGB0419+72
Maffei I
GR8
NGC55
NGC300
NGC253
NGC247
NGC7793
UKS2323-326
NGc45
NGC59
IC342
NGC7252