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Abnormal Profiles in the Low Balmer Lines in Walker 90/V590 Mon

M.R. PИrez (Los Alamos National Laboratory), M.E. van den Ancker (European Southern Observatory), M.D. Joner (Brigham Young University), and B. McCollum (Spitzer Science Center)
OBSERVATIONS & ANALYSIS
Echelle data were taken at Mt. Palomar 60-inch telescope from November 2002 to March 2003. The resolution used was R=19,000 (= 0.2-0.5 е) from 3600- 9000 е

ABSTRACT

H

H

Highly Variable Balmer Lines
a) Inverse P-Cygni Profiles
H and H present consistent IPC profiles in their emissions with red-displaced absorption components

Recent detections of rapid variability in most lines observed (3600 to 9000 е, resolution = 0.2-0.5 е), in the enigmatic Herbig Be star Walker 90/V590 Mon located in NGC 22664, revealed a well-developed inverse P-Cygni (IPC) profile in H and a broad emission in H with a superimposed strong IPC. These profiles seldom appear in the low Balmer emission lines and they have been observed only in a handful of young objects. Moreover, in Walker 90 the historical photometric variability seems erratic with no clear correlation between the colors and the brightness variations for the last 45 years, suggesting that the light variations are not attributable to variable circumstellar extinction. Archival and recent observations will be presented in an effort to advance our understanding on the evolutionary status of this object.

BASIC FACTS
H, H and H present red-displaced absorption components with extended wings of up to 400 km/s

b) Asymmetric Absorption Lines

ID: V590 Mon/Walker 90/NGC 2664-62

RA/DEC (2000): 06 40 44.6 +09 48 03

What is the interpretation?
Low Balmer lines (H and H) showing prominent red-shifted absorption components with terminal velocities in excess of 400 km/s, suggesting the presence of circumstellar material moving away in the line-of-sight.

V = 11.88 ­ 12.94 (1)

Spectral Type: B8-B9.5

Location: NGC 2264 ­ Mon OB Distance: 700 - 950 pc

1) Normally IPC profiles are considered an indication of mass accretion onto the star 2) Variable red-displaced absorption is considered arising from material falling back toward the star, after being ejected at less than the escape velocity

DISCUSSION
IPC profiles seldom appear in low Balmer emission lines (2) (e.g., H and H in our object). However, a small number of HAeBe (11%) and T Tauri (7%) stars have been found to present IPC profiles in H (3). Other studies have shown an even larger number of T Tauri stars (60%) present IPC profiles in Balmer lines (4) by properly subtracting underlying photospheric emissions. Are there any correlations with other observable features? It has been suggested that UXOR activity appears correlated with the presence of IPC profiles (5). We also find that Walker 90 presents a weak photometric blueing effect as the object gets fainter. This property is shared with the other two Herbig Ae/Be stars that also presents IPC profiles, namely UX Ori and BF Ori. IPC profiles in H are usually attributed to its optical thin nature, leading to the conclusion of a highinclination angle of the relic disk (2). Furthermore, in the case of the IPC profile in H in the Tauri star T Cha, it is deduced that low-density in the residual circumstellar material is present in the line-of-sight which is consistent with the presence of a jet system (6). IPC profiles in other lines, like Na D, have been suggested to indicate the presence of magnestopheric accretion (7), which is a mechanism applied to interpret infall in the low-mass T Tauri stars.

REFERENCES
1. 2. 3. De Winter, D. et al. 1002, A&A, 379, 564 Li, J.Z. & Rector, T.A. 2004, ApJ, 600, L67 Reipurth B. et al. 1996, A&AS, 120, 229

H

H

H

4. 5. 6. 7.

Edwards S. et al, 1994, AJ, 108, 1056 Grinin, V.P., Rostopchina, A.N. 1996, Astron. Rep. 40, 171 AlcalА, J.M. et al. 1993, A&A, 272, 225 Sorelli, C. et al. 1996, A&A, 309, 155

Balmer lines (H, H and H) showing strong red-shifted absorption components with terminal velocities of up to 400 km/s, suggesting the presence of circumstellar material moving away in the line-of-sight. Similar asymmetric absorptions are also present in metallic lines like Ca II k.