The excess emission in Classical T Tauri Stars

1
The excess emission in Classical T Tauri Stars

• Jorge Filipe S. Gameiro
• DMA, Faculdade de Ciências Universidade do Porto
• Centro de Astrofísica da Universidade do Porto
  (CAUP)

Collaborators Daniel Folha, Vitor Costa
(CAUP) Nuria Calvet (CfA), Rui Azevedo
(CAUP/CfA) Peter Petrov (Crimean Astrophysical
Observatory)
2
Outline

• Star disc interaction
• Magnetospheric accretion models to fit the excess
  emission (veiling) dependence on wavelength
• Accretion rate determination
• The inner disc structure
• Combine NIR and optical observations
• What is the connection between optical and NIR
  excesses?
• Short time scale variability Inhomogeneous
  accretion

3
I Star-disc interaction

• RU Lupi CTTS
• HR7368 template (K7V)
• RX1524.0-3209 WTTS (K7V)

4
Veiling Measurement procedure
DI Cep (G8IV-V) Template (G8V)
Fe II (l4924)
Residual spectrum
5
Veiling dependence on wavelength DI Cep

• Steep rise clearly seen around 4500 ?
• Veiling tends to increase towards short
  wavelength
• Veiling increase towards near infra-red ?
• Hump feature centred at 5300 ? and about 500 ?
  wide (also reported by Stempels Piskunov 2003)

6
Magnetospheric accretion shock models
optical

• Camenzind 1990, Konigl 1991, Shu et al. 1994
• Magnetospheric accretion models have been
  successful in explaining the excess emission
  (continuum and lines) Calvet Gullbring 1998,
  Gullbring et al. 2000 (BP Tau)
• Parameters of model
• Excess spectrum depends mostly on energy flux of
  the accretion flow F and the projected surface
  coverage of the accretion column f

(Calvet Gullbring 1998, Ardilla Basri 2000)
7
Veiling dependence on wavelength DI Cep
1999 July 28
In agreement with results found from UV data
(Gómez de Castro Fernandes 1996)
8
II-The inner disc structure

• NIR continuum excess is higher than predicted by
  simple models (Folha Emerson 1999, Johns-Krull
  et al. 2001)
• NIR emission arises from an inner disc rim at
  the dust sublimation radius (Natta et al. 2001,
  Muzerolle et al. 2003)

9
Simultaneous observations in the NIR and optical
bands

• South hemisphere (ESO)
• NIR NTT (SOFI) cover the 0.9-2.5mm wavelength
  range
• Optical 1.52m Boller Chiven spectrograph
  (low resolution)
• 27 CTTS, 9 WTTS
• North hemisphere (La Palma)
• NIR TNG
• Optical WHT (ISIS) spectral coverage 3600-9000
  A
• 16 CTTS, 8 WTTS

10

• CTTS span a large range of excess emission
• WTTS used to derive the excess emission spectra.
  They spectral type cover those of CTTS in the
  sample
• The spectra are calibrated in absolute flux
• The observations allow us to determine the
  spectrum of excess continuum from the blue ,
  where emission from the shock dominates, to the K
  band, where emission from accretion disc starts
  dominating

Disentangle the various source of excess emission
11
grisms
T2400K
6200

• 
  Dereddened flux
• Measure veiling at 6200 A (r4.0)
• Scale template spectrum
• Get absolute excess emission

12
Absolute excess emission

• With these observation we relate excess continua
  from the blue to the NIR. Adjust various
  component to the obtained spectra, namely those
  resulting from accretion shock and accretion disc
  models
• Two independent way to determine mass acretion
  rate (accretion shock component from optical
  observations, Pab and Brg line fluxes Muzerolle
  et al. 1998)

13
Veiling excess
6200

• Veiling determined from the absolute fluxes of
  star and template
• Veiling increase towards NIR wavelength.
• Bump at 5300 A due to molecular absorption band
  (TiO)

Veiling 4 at 6200 ?
14
III Accretion rate variability in short time
scales

• BP Tau Observations
• Double arm spectrograph ISIS on the WHT
• Narrow slit (1) ?v6 km/s (blue arm)
  ?v20 km/s (red arm)
• One hour long time series ?t5 min. (blue arm)
  ?t1 min. (red arm)

15
BP Tau

• Classical T Tauri star, K7
• Teff4055 112 K
• Log g 3.67 0.50
• v sini 10.2 1.8 km/s
• i 28º 2º Dutrey, Guilloteau Simon (2003)
• Photometric period 6.1 8.3 days
• Irregular short time scale variability

Johns-Krull, Valenti Koresko (1999)
16
Lines variability
Ha
He I (l6678)

• Ha displays a decrease in intensity and
  significant narrowing at the base
• He I reveals the presence of an inverse P Cygni
  profile on the first 12
• minutes that disappears
• The veiling decreases

17
1 hour

• Variability can be due to
• Obscuration by circunstellar material But
  veiling variations !
• Flare like event possible but the likelihood of
  catching a flare in one hour is very small,
  Gullbring et al. 1996 found no pronounced flare
  activity on BP Tau
• Rotational modulation P6.1-8.3 days
• Accretion rate variation Inverse P Cygni He I

18
Model fits BP Tau data set
M0.5 M?, R2 R?, Teff 4000 K (no Av assumed)
2-component models (2C) pair of log F
1-component models (1C) single log F
19
log F 11.5
log F 10.5
log F 11.0
1C
1C
log F 10.5 log F 11.0
log F 10.5 log F 11.5
log F 11.0 log F 11.5
2C
2C
20
Inhomogeneous accretion

• The accretion rate starts off at relatively high
  value
• Decrease in 1 hour to