A New Group of DustForming Hot Stars

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A New Group of Dust-FormingHot Stars

• Anatoly Miroshnichenko

Pulkovo Observatory (Saint-Petersburg,
Russia) Max-Planck-Institut fur Radioastronomie
(Bonn, Germany) University of Toledo (Ohio, USA)
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Collaborators
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Main Subject

• Dust-Forming Stars

circumstellar ? interstellar ? circumstellar
Hot stars Teff ? 10000 K Shielding from
UV Colliding Winds
Cool Stars Teff 3000 K Strong Outflow
Dust Tsub 1500 K
AGB post-AGB
WR, LBV ? L/L? 105
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Outline

• Early-Type Stars with Circumstellar Dust
• Be Stars
• Properties of Be Stars with Warm Dust
• Search for New Candidates and Results of the
  Initial Observations
• Nature and Evolutionary State
• Conclusions

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Objects with Circumstellar Dust which Include a
Hot Star

• Herbig Ae/Be stars (warm cold dust)
• Vega-type stars (cold dust)
• Symbiotic Stars (M-giant OB-subdwarf, white
  dwarf, or neutron star warm dust)
• VV Cep stars (M-supergiant OB dwarf ? warm
  dust)
• Wolf-Rayet stars (carbon-rich or binary warm
  dust)
• Luminous Blue Variables (cold dust)
• Proto-Planetary Planetary Nebulae (cold dust)
• Be stars

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Be Stars History of Studies

• Discovery Allen Swings (1976, AA, 47, 293)
• 65 objects with forbidden lines and IR excesses
  at ?2 ?m

• Possible explanations for the phenomenon
• Formation of a Planetary Nebula
• Interaction of an OB star with a cool companion
• Direct ejection of matter by a massive OB star

Follow up classification Herbig Ae/Be stars (7),
LBV (3), PNe (17), symbiotic (8), supergiants (7)
28 objects uncertain classification
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Additions and Systematization

• Lists of similar objects
• Carlson Henize (1979, Vistas in Astronomy, 23 ,
  213) 20 early-type stars with strong
  emission-line spectra
• Dong Hu (1991, Chin. AA, 15, 275) 200
  early-type stars with strong IR-excesses
  (IRAS,V-25 8 mag)

Systematization Attempt Lamers et al. (1998, AA,
340, 117) 5 categories of Be stars sgBe,
pmsBe, cPNBe, SymbBe, unclBe
New group of unclBe Be stars with warm dust
BeWD
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IRAS color-color diagram
? - BeWD, ? - ??/?? stars, ? - Vega-type stars,
? - symbiotic stars, - VV Cep
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Be Stars with Warm Dust (BeWD)

• Selection Criteria
• Spectra early-type strong Balmer emission
  lines
• IRAS colors ?0.5
• ?1.1 ?0.3

Presentation as a group Sheikina,
Miroshnichenko, Corporon 1999 (IAU Coll. 175,
Alicante, Spain) - 11 objects Miroshnichenko,
Bjorkman, Chentsov, Klochkova 2002 (IAU Coll.
187, Florida, USA) - 19 objects Miroshnichenko
et al. 2004 (203 AAS Meeting, Atlanta, USA) 19
objects 28 candidates
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Observations
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Properties of BeWD
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Spectral Energy Distribution
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Photometric Properties

• Frequently observed objects
• HD 45677, HD 50138, MWC 300, MWC 342, CI Cam

• Variability Types
• Short-term irregular ?V 0.1 0.5 mag
• Long-term gradual brightness changes ?V 0.5
  2 mag (MWC 342, HD 45677)
• Short-term outbursts ?V 3 mag (CI Cam, 1998
  March 31)
• Cyclic from weeks to years
• Near-IR variations ?K 0.5 mag

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Spectral Properties

• Strong and variable Balmer emission lines

• H? line profiles are mostly double-peaked

• Single- or double-peaked narrow metallic emission
  lines (FWHM 100 km s-1)

• Forbidden lines O I 6300 6364A, N II
  5577, 6348, 6384A, sometimes S III 6312A

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Spectrral Variations
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H? Line Profiles
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Absorption Lines
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IR Spectra
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Basic Physical Parameters

• Spectral Type of the Hot Companion O9-B8
• Spectral Type of the Cool Companion F, K
• Initial Mass 2 - 40 M?
• Luminosity 500 106 L?
• Circumstellar Gas distribution disk-like
• Circumstellar Dust distribution not clear
  (probably circumbinary disk)

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Hertzsprung-Russell Diagram
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Nature and Evolutionary State

• Majority of (all?) objects Main-Sequence and
  after
• Known Binary systems
• MWC 623 B2 V K2 III (Zickgraf 2001, AA, 375,
  122)
• CI Cam Be sg black hole? (Miroshnichenko et
  al. 2002, AA, 390, 627)
• AS 381 B1 I K II-III (Miroshnichenko et al.
  2002, AA, 383, 171)
• V669 Cep B5 V K (Miroshnichenko et al. 2002,
  AA, 388, 563)
• HD 327083 B1 I F I (Miroshnichenko et al.
  2003, AA, 406, 673)
• Suspected Binaries
• MWC 342 (Miroshnichenko Corporon 1999, AA,
  349, 126)
• MWC 657 (Miroshnichenko et al. 2000, AAS, 147,
  5)
• HD 85567 Hen 1398 (Miroshnichenko et al. 2001,
  AA, 371, 600)
• MWC 300 (Miroshnichenko et al. 2004, AA, 417,
  731)
• Objects with a Controversial State
• HD 45677 HD 50138 suggested Herbig ?? stars

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Enlarging the Group
Basis for a new search for BeWD in the IRAS
catalogs

• Stars of the main group are relatively bright
  V 9?12 mag, K 3?7 mag,
  12?m 0?3.5 mag. The IRAS sensitivity
  limit 6 mag
• Large range of the luminosities
• Release of the deep sky surveys in 2003 2MASS
  (JHK) and USNO-B1.0 (5 non-standard optical bands)

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Search Strategy Difficulties

• Selection criteria
• Color-indices 12?25 25?60
• Close positions in the IRAS 2MASS catalogs
• Selection of the brightest 2MASS object in the
  IRAS error box
• Positional coincidence in the 2MASS USNO
  catalogs

• Difficulties
• Selection criteria are only positional
  photometric
• Separation of reddened hot stars from cool
  stars
• Confusion with RV Tau stars

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New Photometric Criterion
? BeWD new candidates
? - RV Tau - cool stars
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Search Results

• ? 4500 IR sources was found in the BeWD box
• 60 objects satisfying the selection criteria were
  found among ?2500 objects with ?b? ? 50?
• ? 20 objects are thrown out after comparison with
  dusty RV Tau stars
• Initial observations of 40 BeWD candidates have
  been started
• Multicolor optical photometry
• Optical spectroscopy of low- and high-resolution
• Low-resolution IR spectroscopy

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Results of the Initial ObservationsSeptember
2003 April 2004

• Photometry
• (WBVR, UBVRI) - 10 objects
• Spectroscopy
• DSO ??3800?5600 A, R1800 10 objects
• ??? ??5200?6600 A, R60000 2 objects
• CFHT H?, SiII 6347, Na D, R100000 11 objects
• Lick Obs. ??0.8 ? 2.5?m, R1300 5 objects
• NASA IRTF ??3 14 ?m, R100 2 objects

It is shown that 8 objects are indeed B/A stars 2
new emission-line objects have been found
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New Objects
IRAS 004706429
BTA
USNO, 2MASS, IRTF
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New Objects
CFHT
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Positional Distribution
? - main group objects, ? - new candidates
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Conclusions

• A new large group (61 objects to date) of hot
  stars with circumstellar dust is discovered

• Dust formation seems to be either on-going or has
  stopped recently

• Objects either binary systems undergoing a rapid
  mass exchange or single stars with unusually
  strong winds

• Investigation of the group may lead to new ideas
  for evolutionary theories of single/binary stars
  and refinement of our understanding of dist
  formation