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Summary of Experiences from
Observations of the Bebinary
 Sco
Anatoly Miroshnichenko
University of North Carolina at Greensboro
USA
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Properties of Be Stars
Basic Parameters of the  Sco System
Observed Behaviour of the System
Conclusions That Can Be Made Now
Properties of Be Stars
Definition:
Be stars are rapidly rotating non-supergiant objects of
spectral type B that sometimes show hydrogen
emission lines in their spectra
Spectral type: O9 – A1 (Teff : ~30000  9000 K)
Luminosity: 100 – 3 104 Lʘ
Projected rotation velocity (v sin i): up to break-up
Vbreak-up = 436 (M/Mʘ)1/2(R/Rʘ)1/2 km/s
Basic Stellar Parameters
Evolutionary
tracks for single
stars (numbers
are initial masses
in Mʘ)
Zero-age mainsequence
Circumstellar Disks of Be Stars
Properties:
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Flat near the star
Disk thickness increases outward from the star
Density drops with distance from the star as rn
Density exponent n ~ 2.54.0 (simplified models)
Disks are temporary (can be present for decades)
Disks can suddenly appear or disappear
Disks can change into rings
Disks can add to the continuum brightness (up to
70% in the optical region)
Theoretical Disk Structure
Carciofi & Bjorkman (2004, Polarization Conf., Hawaii)
Reasons for the Be Phenomenon
Rapid rotation can be intrinsic (from birth) or
induced (mass-transfer in a binary system)
Mass loss (disk formation) can be triggered by
pulsations or by close passages in binaries
Disk material orbits the star moving outward
through viscosity
If mass loss from the star exceeds mass loss from
the disk, the material is accumulated near the star
Hypotheses about the Nature of
the Be phenomenon
In a binary system, the
mass gainer spins-up to
critical rotation (Křiž &
Harmanec 1976, Bull.
Astr. Inst. Czekh., 26, 65)
Non-radial pulsations may be a
triggering mechanism for the
mass loss from at least earlytype Be stars (Rivinius et al.
2003, A&A, 411, 229)
Non-Radial Pulsations
Line Formation in Disks
McDonald Observatory
R=60000
Disk Size Effects
Continuum Excess Radiation
1998
small
or no
disk
Opt+IR
UV
 Aqr
1983
large
disk
 Scorpii
R.A. 16h 01m, Dec. 2238 (J2000)
Parameters of  Sco
Optical brightness without disk, V=2.32 mag
Spectral type B0.3 IV
Distance, D = 12315 pc
Luminosity, log L/Lʘ = 4.40.1
Surface temperature, Teff = 27500500 K
Surface gravity, log g = 4.0 (typical for a dwarf)
This is a binary system with an angular separation
at apoastron of 0.2 arcseconds
Orbital period, P = 10.60.1 years (uncertain)
Eccentricity, e = 0.940.01
Secondary, V ~1.5 mag, Sp.T. ~B3 (uncertain)
 Sco without Disk
Orbit of  Sco
Average
radial
velocities of
the H
emission line
Orbit of  Sco
Brightness Variations of  Sco
Brightness Variations of  Sco
 = 0.5 m
 = 2.2 m
Recent Brightness Variations
H line in 20002003
Disk in 2001
From Carciofi et al. (2006, ApJ, 652, 1617)
Disk in 2001
H line in 20042007
H EW Evolution
Brightness  Spectrum
H Line Width Drop
Seen
since
March
2005
CII, CIV
Line
emission?
Possible Explanations
The brightness decrease in 2004/5 can be due to a
decreasing mass loss from the primary
The disk became a ring
Observed consequences:
The H line width decreased (no contribution
from rapidly rotating part of the disk)
The line equivalent width (EW) decreased
What to Expect at Periastron
Current disk size is ~ 20 R1 or ~ 150 Rʘ
It may grow larger as time goes
Distance between the stars at periastron is d = 24 R1
Primary’s Roche lobe size ~ 0.6 d or ~ 15 R1
Consequences:
Some disk material may flow into the secondary’s
Roche lobe
Disk may become denser and line emission will rise
Single- or triple-peak profiles may be observed
Roche Lobes
Conclusions and Suggestions
• The binary is coming to its next periastron in
February  May 2011 (observable from the
Northern hemisphere)
• Weekly observations are important before
periastron and more frequent around it
• Photometry needs to accompany spectroscopy
• Radial velocity data will constrain the orbital
period
• Impact of the Roche lobe compression on the disk
may be revealed