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