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 Star disc interaction Magnetospheric accretion models to fit the excess emission (veiling) dependence on wavelength Magnetospheric accretion models to fit the excess emission (veiling) dependence on wavelength Accretion rate determination Accretion rate determination The inner disc structure The inner disc structure Combine NIR and optical observations Combine NIR and optical observations What is the connection between optical and NIR excesses? What is the connection between optical and NIR excesses? Short time scale variability – Inhomogeneous accretion 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 Fe II (  DI Cep (G8IV-V) Template (G8V) Residual spectrum

5. Veiling dependence on wavelength – DI Cep OHP (ELODIE) / 1997 WHT (UES) / 1999 NOT (SOFIN) / 2001 Steep rise clearly seen around 4500 Ǻ Veiling tends to increase towards short wavelength Veiling increase towards near infra-red ? Hump feature centred at 5300 Ǻ and about 500 Ǻ wide (also reported by Stempels & Piskunov 2003)

6. Magnetospheric accretion shock models Camenzind 1990, Konigl 1991, Shu et al. 1994 Camenzind 1990, Konigl 1991, Shu et al. 1994 Calvet & Gullbring 1998, Gullbring et al. 2000 (BP Tau) 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 – 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 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) Accretion column Hot spot Disc Dust and gas Disc gas (Camenzind 1990) NIR FIR optical

7. Veiling dependence on wavelength – DI Cep 1999 July 28 In agreement with results found from UV data (Gómez de Castro & Fernandes 1996) Results

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) Accretion column Hot spot Disc Dust and gas Disc gas (Camenzind 1990) NIR FIR

9. Simultaneous observations in the NIR and optical bands South hemisphere (ESO) South hemisphere (ESO) NIR – NTT (SOFI) [cover the 0.9-2.5 m m wavelength range] NIR – NTT (SOFI) [cover the 0.9-2.5 m m wavelength range] Optical – 1.52m [Boller & Chiven spectrograph (low resolution)] Optical – 1.52m [Boller & Chiven spectrograph (low resolution)] 27 CTTS, 9 WTTS 27 CTTS, 9 WTTS North hemisphere (La Palma) North hemisphere (La Palma) NIR – TNG NIR – TNG Optical WHT (ISIS) [spectral coverage 3600-9000 A] Optical WHT (ISIS) [spectral coverage 3600-9000 A] 16 CTTS, 8 WTTS 16 CTTS, 8 WTTS

10. CTTS span a large range of excess emission 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 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 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 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. T=2400K 6200 1. = Dereddened flux 2.Measure veiling at 6200 A (r=4.0) 3.Scale template spectrum 4.Get absolute excess emission grisms

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, Pa  and Br g 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 Ǻ

14. III – Accretion rate variability in short time scales BP Tau Observations BP Tau Observations Double arm spectrograph ISIS on the WHT Narrow slit (≈1”) Δv≈6 km/s (blue arm) + Δv≈20 km/s (red arm) One hour long time series:Δt≈5 min. (blue arm) + Δt≈1 min. (red arm)

15. BP Tau Classical T Tauri star, K7 Classical T Tauri star, K7 Teff=4055 ±112 K Teff=4055 ±112 K Log g = 3.67 ±0.50 Log g = 3.67 ±0.50 v sini = 10.2 ± 1.8 km/s v sini = 10.2 ± 1.8 km/s i = 28º ±2º Dutrey, Guilloteau & Simon (2003) i = 28º ±2º Dutrey, Guilloteau & Simon (2003) Photometric period = 6.1 – 8.3 days Photometric period = 6.1 – 8.3 days Irregular short time scale variability Irregular short time scale variability Johns-Krull, Valenti & Koresko (1999)

16. Lines variability HH  e I ( 6678) H  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. 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 – P=6.1-8.3 days Accretion rate variation – Inverse P Cygni He I 1 hour

18. Model fits BP Tau data set: M * =0.5 M , R * =2 R , T eff = 4000 K ( no A v assumed ) 1-component models (1C) single log F 2-component models (2C) pair of log F

19. log F =10.5 log F =11.0 log F =11.5 log F =10.5 log F =11.0 log F =10.5 log F =11.5 log F =11.0 log F =11.5 1C 2C  observations  model results 1C 2C

20. Inhomogeneous accretion The accretion rate starts off at relatively high value The accretion rate starts off at relatively high value Decrease in 1 hour to Decrease in 1 hour to