Transcript Quantum Well Electron Gain Structures and Infrared

Multi-Epoch Star Formation?
The Curious Case
of
Cluster 1806-20
Stephen Eikenberry
University of Florida
11 April 2007
SGR 1806-20
• Soft Gamma-Ray
Repeater – highlymagnetized (B ~1015 G)
neutron star
• Radio nebula (not SNR)
• Chandra X-ray position
 IR-identified cluster of
massive stars (Eikenberry et al.,
2001; Kaplan et al., 2002)
• ISO images  still
embedded in molecular
cloud (Fuchs et al., 1999)
• Large LOS reddening
(AV ~30 mag)
Cluster 1806-20
• Several luminous OB
supergiant stars
• Multiple Wolf-Rayet stars
of various types
• Two WC9d stars (~10% of
the known Galactic
population)
• SGR is near edge of
cluster core (“x”)
• Brightest star is Luminous
Blue Variable (source of
radio nebula)
• Projected image size ~3pc
on a side (!!)
Distance
• CO & Galactic rotation  distance to molecular clouds
• AV, NH & CO suggest “far” distance for cluster
• Radio source shows NH3 absorption from MC73
 d = 15.1 (+1.8, -1.3) kpc (Corbel & Eikenberry, 2004)
LBV 1806-20
• IR spectra give extinction, temperature (velocity
consistent with MC)
• With distance  L > 4x106 L0 (similar to Eta Car and
Pistol Star)
• Implies mass > 150 M0 (Eddington-based)
• Not a cluster; is it a binary?? Even if binary,
minimum mass > 75 M0
• So …
• SGR = neutron star already; if same birthdate,
progenitor must have been more massive than LBV
• But, stars > 75 M0 don’t make neutron stars (??;
max progenitor mass < 25 M0)
• Could be multi-epoch SF?
Is LBV 1806-20 that big?
• Figer et al., 2004 find
double-lined spectra 
binary? (or wind
structure??)
• Assume vsys = vmid
• Then, Galactic rotation
implies d = 11.7 kpc
• Claim this is “strong
difference” from
Eikenberry et al. 2004
(but no error bars in
Figer et al. 2004 …)
Reduced Distance Means …
• Lower luminosity, thus lower mass (130 M0)
• Binary implies 65 M0 lower limit on most massive
star
• Figer et al. (2005)  near-IR spectra of several highmass stars in cluster
• Claim consistent with single age = 3-4 Myr & SGR
progenitor > 50 M0
• No need for multi-epoch SF (?? – still » 25M0 ; plus,
why did 50 M0 star blow up before 65 M0 star? …)
Is LBV 1806-20 that close?
• Figer et al. give no
uncertainties (!); d ~
2.5 (only “Eikenberry” error
bars)
• Figer used mismatched
GC distance; correct that
 d = 12.5 kpc
(difference now <2)
• Also, vmid assumes that
the binary mass ratio
q = 1.000 (not necessarily
true!)
• Model spectra  q  1-5
(Lavine, Eikenberry, Smith)
Is LBV 1806-20 that close?
• d = 10.7 – 18.1 kpc
 consistent with
(fully encompasses)
original distance
• Center of range =
14.4 kpc (~0.5 of
“Eikenberry-only”
error bars)
• Also, Figer et al distance implies that both WC9d
stars are least luminous in their class (anywhere!)
• Assume WC9d here has minimum luminosity of any
other known WC9d  d> 15 kpc
Back to Multi-Epoch SF?
• Original distance more robust than others, but
consistent with all (once you put in error bars!)
• MLBV > 150 M0 total; >75 M0 for binary
• More: we see major LBV line variability (factors of
~5-6 variation in EW in 1 year)  implies that one
star is dominant source of ionizing radiation
• Thus, even if it is a binary, probable q>1 and mass
limit >> 75 M0
• (And … something BIGGER made a neutron star
???)
• Single birthdate starting to stretch the imagination
(if not smoking gun, at least “smoldering slingshot”)
The Smoking Gun (??)
• MIRLIN IRTF
observations
• N1  LBV and WC9 star
• N4 & N5 central source
• Qs  13 Jy point source
(!!); embedded protostar?
• Qs luminosity > Lbol for
20 M0 star  massive
protostar
• NS progenitor born >2-3
Myr ago
• This object <1 Myr old
Conclusions
• Cluster 1806-20 is a rich/weird environment: SGRs,
WRs, LBVs, etc., all within R<1 pc
• Best distance estimate (still) 15.1 kpc
• LBV 1806-20 is a very luminous/massive star(s?)
• Either a star > 75 (150) M0 made a neutron star, or
we have multi-epoch star formation here
• Apparent embedded massive protostar with much
younger age independently suggests MESF
• One idea: NS progenitor forms, explodes near cloud
edge; SN shock penetrates cloud and triggers burst
of SF – particularly, unusually massive stars (???)