A spectroscopic study of U Mon an RV Tau-type post-AGB star Osamu Hashimoto 1 , Satoshi Honda 2 , Hikaru Taguchi 3 , & Kazuo Yoshioka 4 1 Gunma Astronomical Observatory, Japan 2 Kwasan Observatory, Kyoto University , Japan 3 Gunma Lifelong Learning Center, Japan 4 The Open University of Japan
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A spectroscopic study of U Mon an RV Tau-type post-AGB star Osamu Hashimoto 1, Satoshi Honda 2, Hikaru Taguchi 3, & Kazuo Yoshioka 4 1 Gunma Astronomical.
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A spectroscopic study of U Mon an RV Tau-type post-AGB star
1 Gunma Astronomical Observatory, Japan 2 Kwasan Observatory, Kyoto University , Japan 3 Gunma Lifelong Learning Center, Japan 4 The Open University of Japan
Abstract
We have made spectroscopic observations of an RV Tauri-type variable star U Monocerotis ( U Mon ) since 2008 with the use of the high resolution echelle spectrograph GAOES on the 150 cm reflector at Gunma Astronomical Observatory ( GAO ) in Japan. The profile of the Hα line varies in a complicated manner through the observation period. There are some absorption components with a narrow line width less than a few angstroms in a broad emission component which disappears sometimes. It is probable that some narrow emission components may also exist over the broad emission in some occasions.
GAOES on the Gunma 150cm reflector
U Monocerotis ( HD13775 )
RV Tauri-type variable star P ~ 92 days mv ~ 5.1 - 7.1 mag Sp. type : F8eIb ( max ) - K0pIb ( min ) [ group A] RVb ~ 2475 days Post-AGB Low mass star ( m ~ 1 Mo ) AGB( asymptotic giant branch ) ➔ PN( planetary nebula )
Observations
GAOES ( Gunma Astronomical Observatory Echelle Spectrograph ) Gunma 150cm reflector R = λ / δλ ~ 70000 wavelengths : 482 nm - 660 nm ( one exposure coverage ) exposure : ~ 60 min - 120 min S/N > 100 14 January 2008 - 16 March 2010 ( JD 2454480 - 2455271 ) 9 cycles ( P ~ 92 days )
Light curve ( from AAVSO )
1 2 3 4 5 6 7 *cycle
8 0
*cycle : counted as phase = 1.0 at the primary minimum in February 2008
Hα feature time variation
1. Broad emission component FWHM ~ 0.5 nm ? very weak or almost disappears sometimes ( cf. 20080308 phase 1.42 )2. Narrow absorption components FWHM < 0.2 nm a few independent components independent of the broad emission component3. Narrow emission components ? may appear in some occasions observed only in the period of phase 4.75 - 5.84 ( see 20090402 phase 5.65 )
Tim
e ( phase )
Variation of Hα feature of U Mon
phas
e
Variation of Hα feature of U Mon
- Broad emission component - Dependence on phase
- Absorption components - Dependence on phase ( sum of all the absorption lines )
- Radial velocity of the broad emission component - Dependence on phase
- Velocity of the main absorption component - Dependence on phase ( against the broad emission )
1. Broad emission component
strong around the phase ~ 0.0 ( primary minimum ) at the phases of ~ 0.6 - 0.8 with a rapid increase at ~ 0.7 and a rapid decline after the peak weak at the phases of ~ 0.2 - 0.6 sometimes very weak or almost disappearing mild variation around the phase of ~ 0.0
2. Narrow absorption components
a number of absorption lines ( independent each other ? ) no strong correlation with the phase of RV variation no strong correlation with the broad emission components but, tend to be weak at the phases around 0.6 - 0.8 which may be correlated with the rapid increase of the broad emission component
Summary
3. Radial velocities of the Hα components
the brad width of the emission component corresponds to a velocity of the order of magnitude of 100 km/s
some variations depending on the phase are seen some variations for a longer time scale than the RV period may exist
but more detailed and careful analysis of the data is required