Spectra of the Brightest Be stars and Objects Description

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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

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Be Stars
? Cassiopeae discovered in 1866
Circumstellar gas has a flattened distribution
(disk-like)

• Main Properties
• Intermediate luminosity
• Emission-line spectra
• Rapid rotation

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What Is Unknown?

• How and why the disks evolve?
• Disks seem to disappear completely
• Mass loss rate seems to be variable

• 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

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Spectroscopy of Be Stars at the Ritter Observatory

• 1-meter telescope with a fiberfed echelle
  spectrograph and a 1150x1150-pixel CCD in the
  Coude focus

• 9 non-overlapping orders, 70 Å each, range
  5285?6600 Å. Includes spectral lines of FeII 5317
  6383, HeI 5876, NaI 5889 5895, SiII 6347
  6371, and H?

• Spectral resolving power R (?/??) 26000

• 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
  1991?2007

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? Cassiopeae
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? Cassiopeae
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48 Librae
V 4.8?4.95 mag B4 IIIe D157?17 pc V sin i
400 km/s
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48 Librae
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? Canis Minoris
V 2.9 mag B8 Ve D52?2 pc V sin i 245 km/s
Possible orbital periods 218.5 days and 3
years Both not confirmed
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? Canis Minoris
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? Canis Minoris
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? Canis Minoris
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? Persei
V 4.2 mag B5 Ve D215?30 pc V sin i 212 km/s
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? Persei
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66 Oph
V 4.6 mag B2 Ve D207?40 pc V sin i 240 km/s
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66 Oph
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? Cassiopeae
V 4.5 mag B5 IIIe D280?80 pc V sin i 220
km/s
No line emission in 1970-s
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? Cassiopeae
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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

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What We Get Studying Binaries
Most Be binaries are single-lined ? secondaries
are much fainter than primaries The brightness
difference is ?V 2?4 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
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? Aquarii
U?B
V
K
B?V
Polarization
EW (H?)
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? Aquarii
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? Aquarii
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Be Binary Candidates
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How and What to Look For

• Regular low-resolution spectral observations
• search for dramatic variations (new disk
  formation or disappearance)
• monitoring of long-term changes of the line
  strength

Goals of higher-resolution spectroscopy
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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
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Summary

• Monitoring of bright Be star is important for
  finding the reasons for the phenomenon
• Spectral resolution of 5000?20000 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