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Spectra of the Brightest Be stars and Objects Description
Anatoly Miroshnichenko
University of North Carolina at Greensboro
USA
• Observational Features of Be Stars
• Temporal Behavior of Individual Objects
• Bright Objects for Monitoring
Be Stars Cassiopeae
discovered in 1866
Main Properties:
• Intermediate luminosity
• Emission-line spectra
• Rapid rotation
Circumstellar gas has a flattened distribution (disk-like)
What Is Unknown?
Are Be stars single objects or binary systems?
• 25% detected binaries in the brightest 240 Be stars
• Weak-lined objects can be single or close binaries
• Strong-lined objects can be wide binaries
How and why the disks evolve?
• Disks seem to disappear completely
• Mass loss rate seems to be variable
Spectroscopy of Be Stars at the Ritter Observatory
• 9 non-overlapping orders, 70 Å each, range 52856600 Å. Includes spectral lines of FeII 5317 & 6383, HeI 5876, NaI 5889 & 5895, SiII 6347 & 6371, and H
• Spectral resolving power R (/) ~ 26000
• 1-meter telescope with a fiberfed echelle spectrograph and a 1150x1150-pixel CCD in the Coude focus
• Spectra of stars brighter than 7.5 mag can be obtained in 1 hour with a signal-to-noise ratio of ~100
•~2000 spectra of ~ 45 Be stars obtained in 19912007
Cassiopeae
Cassiopeae
48 LibraeV ~ 4.84.95 mag
B4 IIIe
D=15717 pc
V sin i ~ 400 km/s
48 Librae
Canis MinorisV ~ 2.9 mag
B8 Ve
D=522 pc
V sin i ~ 245 km/s
Possible orbital periods: 218.5 days and 3 years
Both not confirmed
Canis Minoris
Canis Minoris
Canis Minoris
Persei
V ~ 4.2 mag
B5 Ve
D=21530 pc
V sin i ~ 212 km/s
Persei
66 OphV ~ 4.6 mag
B2 Ve
D=20740 pc
V sin i ~ 240 km/s
66 Oph
CassiopeaeV ~ 4.5 mag
B5 IIIe
D=28080 pc
V sin i ~ 220 km/s
No line emission in 1970-s
Cassiopeae
Orbital period vs. EW (H)+ - Be/X-ray binaries• - B1 4 Be binaries° - B5 8 Be binaries Conclusions:
• Longer orbital period larger disk stronger lines
• Later spectral type smaller ionized disk area weaker lines
What We Get Studying Binaries
Most Be binaries are single-lined secondaries are much fainter than primaries
The brightness difference is V ~ 24 magnitudes
Orbital periods and spectroscopic masses companion separation disk sizes
The main disk responsible for the line emission and IR excess is around the primary companion
The secondary may have some amount of circumstellar matter around it
AquariiV
K
Polarization
UB
BV
EW (H)
Aquarii
Aquarii
Be Binary Candidates
Name V-mag EW(H), AEW Lac 5.4 46
V777 Cas 7.0 2045
V695 Mon 6.5 45
HD 206773 6.9 043
105 Tau 5.9 42
HD 208682 5.9 41
Per 4.2 3040
HD 202904 4.4 32
DX Eri 5.9 30
Gem 4.2 8
How and What to Look ForRegular low-resolution spectral observations:
• search for dramatic variations (new disk formation or disappearance)
• monitoring of long-term changes of the line strength
R=500010000 Patrol for line profile and EW variations
R>10000 Detection of the orbital motion
R>40000 Line profile fine structure
Goals of higher-resolution spectroscopy
Galactic Be Stars
The only catalog of Galactic Be stars – Jaschek & Egret (1982)
It contains 1159 objects down to ~13 mag
About 30% of them may not be Be stars (we only know that they have H emission)
The brightest part of the catalog has been cleaned: there are ~310 Be stars brighter than ~7.5 mag
Fainter ones need to be observed spectroscopically and reclassfied
Summary
• Monitoring of bright Be star is important for finding the reasons for the phenomenon
• Spectral resolution of 500020000 can be enough to search for condition changes in the disk and searching for orbital motion
• Frequency of observations: twice a month when the changes are slow and as frequent as possible when rapid changes occur
• Observations of objects fainter than ~7 mag are important to clean up the existing catalog of Galactic Be stars