T. Le Bertre 1 , M. Tanaka 2,3 , I. Yamamura 2 , H. Murakami 2 , D.J. MacConnell 4 , A. Guertin 1,5 1 Paris Observatory, France 2 Institute of Space and Astronautical Science, Japan 3 National Astronomical Observatory, Japan
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T. Le Bertre1, M. Tanaka2,3, I. Yamamura2,
H. Murakami2, D.J. MacConnell4, A. Guertin1,5
1 Paris Observatory, France
2 Institute of Space and Astronautical Science, Japan
3 National Astronomical Observatory, Japan
4 Computer Sciences Corporation/Space Telescope Science Institute, USA
5 University of Montréal, CanadaNear-infrared spectrophotometry of carbon stars: from the IRTS to dome C
ARENA conference, Paris, 14-16 June 2006
Carbon stars are characterized by the presence of carbon molecules such as C2 or CN. The enrichment in carbon may occur when they evolve on one of the giant branches or may be due to mass transfer from a more evolved companion.
Inventories of cool carbon stars are of special interest because these objects can be used to trace matter at large galactocentric distances out to the Magellanic Clouds.
Carbon stars contribute to the replenishment of the ISM.
We will examine the potential for finding and characterizing carbon stars by using near-infrared spectrophotometric surveys. For that purpose, we use the data provided by the Japanese space experiment IRTS.
The InfraRed Telescope in Space (IRTS) is a 15 cm diameter telescope operated in space which surveyed ~ 7 % of the sky in two strips, one along the galactic plane and the other covering the high galactic latitude region (Murakami et al., 1996, PASJ 48, L41).
The 2 strips covered by the IRTS in galactic coordinates
The IRTS was equipped with four scientific instruments operating in parallel: the Near-InfraRed Spectrometer (NIRS; 1.4-4.0 µm), the Mid-Infrared Spectrometer (MIRS; 4.5-11.7 µm), the Far-Infrared Line Mapper (FILM; 145, 155, 158, 160 µm), and the Far-InfraRed Photometer (FIRP; 150, 250, 400, 700 µm). Most wavelengths observed by IRTS are blocked by the Earth's atmosphere and cannot be observed with ground-based telescopes.
The Near-InfraRed Spectrometer (NIRS) is a low-resolution grating spectrophotometer (Noda et al., 1994, ApJ 428, 363). A 12 x 2 channel InSb detector array covers two wavelength ranges, 1.4-2.5 and 2.8-4.0 µm, with a spectral resolution ranging from ~20, at short wavelengths, to ~40 at the long wavelength end. The entrance aperture was 8 arcmin by 8 arcmin on the sky.
More than 14 000 point sources have been detected. Their spectra can be accessed via the DARTS archive
T Lyr, CGCS 4038 operating in parallel:Mass losing carbon stars can be easily identified from the deep absorption band at 3.1 µm.
NIRS spectra of
cool carbon stars show
molecular absorptions at
1.4 µm (CO + CN),
1.8 µm (C2),
2.3 µm (CO),
3.1 µm (C2H2+HCN) and
3.8 µm (C2H2).
By contrast, NIRS spectra
of late-type, oxygen-rich stars show only CO and H2O bands,
in particular at 1.9 µm.
increasing depth of the 3.1 µm feature
We have identified 139 cool carbon stars in the NIRS survey of the IRTS from the conspicuous presence of molecular absorption bands at 1.8, 3.1, and 3.8 µm (Le Bertre et al., 2005). Among them, 14 are new, bright (K ~ 4.0-7.0) carbon stars; two such cases are shown below. Some dusty carbon stars, like NIRS 07036-2221, can only be revealed by infrared surveys.
The IRTS data show a clear spatial separation in the Galactic Plane between mass-losing, oxygen-rich stars and mass-losing, carbon stars, with the former (dots) outnumbering the latter (diamonds) for rGC< 8 kpc, and the reverse for rGC> 10 kpc.
ISO/ SWS: 3-8 µm; operating in parallel: R ~200-1000
Aoki et al. 1999, IAUS 191, 175
Y CVn; KAO operating in parallel:
CN bandhead @1.40 µm
C2 bandhead @1.77 µm
Goebel et al. 1980, ApJ 235, 104
IRTS/ NIRS operating in parallel: : UV Cam; CGCS 177 (R8)
CN bandhead @1.40 µm
C2 bandhead @1.77 µm
Le Bertre et al. 2005, PASP 117, 199
+ possibility of
For galactic carbon stars important tool :
Request important tool :
An atmospheric transmission (and if possible emission during day and night) from Concordia in the range 1.2-4.1 µm, in order to determine which part of the spectrum can be accessed from dome C.
An integral-field spectro-imager, R ~ 80-100, operating from
1.2 to 4.0 µm that would allow to explore an area that has
been barely touched by the IRTS.
Spectrophotometric imaging surveys: important tool
General resource for the study of stars, stellar structures and ISM
L’ important tool
H20 = 1mm; 1 ai
Modelled atmospheric transmission from Antarctica “dome C”
For the IRTS carbon stars, we find a trend relating the 3.1 µm band strength to the K-L’ color index, which is known to correlate with mass-loss rate.
The 14 new carbon stars are represented by a ‘ ’