A spectroscopic study of u mon an rv tau type post agb star
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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 Observatory, Japan 2 Kwasan Observatory, Kyoto University , Japan

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A spectroscopic study of U Mon an RV Tau-type post-AGB star

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A spectroscopic study of u mon an rv tau type post agb star

A spectroscopic study of U Mon an RV Tau-type post-AGB star

Osamu Hashimoto1, Satoshi Honda2,

Hikaru Taguchi3, & Kazuo Yoshioka4

1 Gunma Astronomical Observatory, Japan

2 Kwasan Observatory, Kyoto University , Japan

3 Gunma Lifelong Learning Center, Japan

4 The Open University of Japan


A spectroscopic study of u mon an rv tau type post agb star

Abstract

We have made spectroscopic observations of an RV Tauri-type variablestar 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 whichdisappears 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


A spectroscopic study of u mon an rv tau type post agb star

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 )


A spectroscopic study of u mon an rv tau type post agb star

*cycle : counted as phase = 1.0

at the primary minimum

in February 2008

Light curve ( from AAVSO )

*cycle

0

1

2

3

4

5

6

7

8


A spectroscopic study of u mon an rv tau type post agb star

Hαfeature 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 component

3. Narrow emission components ?

may appear in some occasions

observed only in the period of phase 4.75 - 5.84

( see 20090402 phase 5.65 )

Time ( phase )


A spectroscopic study of u mon an rv tau type post agb star

VariationofHαfeature of U Mon

phase


A spectroscopic study of u mon an rv tau type post agb star

VariationofHαfeature of U Mon


A spectroscopic study of u mon an rv tau type post agb star

- Broad emission component -

Dependence on phase


A spectroscopic study of u mon an rv tau type post agb star

- Absorption components -

Dependence on phase ( sum of all the absorption lines )


A spectroscopic study of u mon an rv tau type post agb star

- Radial velocity of the broad emission component -

Dependence on phase


A spectroscopic study of u mon an rv tau type post agb star

- Broad emission component -

Dependence on phase ( absorption corrected )


A spectroscopic study of u mon an rv tau type post agb star

- Velocity of the main absorption component -

Dependence on phase ( against the broad emission )


A spectroscopic study of u mon an rv tau type post agb star

Summary

1. Broad emission component

strongaround the phase ~ 0.0 ( primary minimum )

at the phases of ~ 0.6 - 0.8

with a rapidincrease 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


A spectroscopic study of u mon an rv tau type post agb star

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

4. How to explain or how to understand

complicated very much

we need more studies


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