Young active star research with SONG and mini-SONG Huijuan Wang National Astronomical Observatories Chinese Academy of Charleston

Contents  Young active star  With SONG  With mini-SONG  When SONG + mini-SONG

Why young active star  The past of our Sun  The evolution history of Milky Way  Good targets for extrasolar planets search  Distinguish between variation in frequency caused by oscillation and activities

PTTS CTTS WTTS ZAMS Early evolution of solar-like stars （ Neuhäuser 1997 ）

 M ＜ 2.5M ⊙ （ Late spectral type ）  Early phase of evolution(t<10Myr/100Myr)  Obvious absorption line of Li 6708 Å  Weak emission line of Hα （ EW Hα ≤10Å ）  No circle-stellar disk ( mostly )  Strong soft X-ray emission Characters of WTTS & PTTS

Young active star  Background  Identification of a sample of young solar- type star candidates  Identification of an active spectroscopic binary: HD  Research of two young solar-type stars within 20pc  summary

Background introduction  ROSAT soft X-ray survey  Observational research of WTTS -> central area of Taurus-Auriga (Neuheauser et al 1995; Wichmann et al 2000 )  Observational research of our group  Xinglong group ： Li & Hu 1998  ROSAT bright source catalog & Tycho catalog ＝ > sample of young solar type stars  criterion ： logC + 0.4V (Lx > erg s -1 )  Monitoring observation on 60 cm telescope at Xinglong observation station  WTTS candidates most distributed in the outside region of Taurus—Auriga

Why high resolution?  Identify these YSS candidates  Study the relationship between them and the nearby young groups  Research the relationship between the EW of Li and the rotation period High resolution observations are necessary. （ Wichmann 1996; Martin 1998 ）

Research method  Sample  V< 9.5 mag,63 stars  Observation  2.16m tel & Coude echelle spectrograph(R ＝ ）  Data reduction & analysis  IRAF software (Echelle, Daophot)  Expect results  Equivalent width (EW) of Li  Radial velocity (RV)  Projected rotation velocity  Spectroscopic binary etc.

stars year  23 －－ 2000 & 2001  37 －－ 2004 & 2005  18 －－ 2006  22 －－ 2007  31 －－ 2008 ==>Sample ： 63 stars （ 167spectra ） Spectroscopic observation log

Histogram of EW (Li)

WTTW+PT TS 21 stars 33% ZAMS 20stars 32% MS 22 stars 35% About 2/3 are young stars

Young active star  Background  Identification of a sample of young solar- type star candidates  Identification of an active spectroscopic binary: HD  Research of two young solar-type stars within 20pc  summary

Young low-mass binary  Opportunity to derive precise measurements of the fundamental stellar parameters of their constituent stars ( stellar mass & radius)  Derive calibrations of young-star evolutionary models  Determine the unbiased mass-ratio and orbital-period distribution  The sample of well-studied young low-mass binaries remains small  High resolution spectroscopic observation (powerful technique)  Identify binary  Obtain accurate parameters (mass & mass ratio)

HD  Bright X-ray source (Schwope 2000)  V ＝ 8.81 mag  None hight resolution spectroscopic observations before then  ： show double lines  & ： show shift between lines  till ： totally 45 spectra

Radial velocity curve

Spectral Disentangling  KOREL code (Hadrava 1995)

Photometic varibility   Amplitude:0.057mag  Cased by spots on the primary, but not ellipsoidal distortion  a synchronous system (spots face us / pri -)

Age － method 1

Age － method 2  Age ~ 100 － 150Myr

－ ＝ Subtracted profile Chromospheric activity Observed spectrum Model G9 ＋ K0  Strong chromospheric activity on the primary Emission originates in plage-like regions

Young active star  Background  Identification of a sample of young solar- type star candidates  Identification of an active spectroscopic binary: HD  Research of two young solar-type stars within 20pc  summary

 TW Hya Association(TWA)  TW Hya 20Myr ， 56.4PC The nearest star formation region. （ Zuckerman b. et al 2001 ， 2004 ） Nearby young groups

 11 stars in our sample:  EW(Li) > 100 mÅ  D < 50 PC  So close & so young  early evolution of the sun  understand the structure and the evolution history of the Milky Way  perfect sample for exoplanet survey

stars D<20PC （ Wang & Wei, 2009, RAA, 9, 315 ）

HIP Age (Myr)

Young active star  Background  Identification of a sample of young solar- type star candidates  Identification of an active spectroscopic binary: HD  Research of two young solar-type stars within 20pc  summary

Summary  Finish the identification of a sample comprising 63 stars, and 2/3 of them are young solar-type stars (YSS)  Identify a ZAMS active double lined spectroscopic binary ： HD  Spectroscopic study of two YSS (HIP 544 & HIP ) within 20 pc of the sun

S hortage of these observations  Single site, single telescope  Time gap is big  We need network & continuous observations SONG

With SONG -spectroscopy  Stellar Observations Network Group(SONG)  Eight telescopes (3/8 in progress)  Filling the time gap ( avoid aliasing frequencies)  Astroseismic research of pulsating stars  Astroseismic research of Other objects including young active stars

Astroseismology, C. Aerts,J. Christensen Dalsgaard, D.W. Kurtz

With mini-SONG  Photometry  Multicolor  Simultaneous  Distinguish variation caused by planets and stellar activities  Low frequency oscillation of stars  Primary parameters of stars

When SONG + mini-SONG  Precise spectroscopy + multicolor photometry  Simultaneous!  Distinguish between variation in frequency caused by oscillation and activities  Oscillation evolution of solar like stars along the evolution track ……

What can we do?  For our SONG & mini-SONG  Cooperate shoulder to shoulder  Research, site … Let’s enjoy it !