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New Surprises from the
Microsatellite
… aka the Humble space telescope
MOST Parameters
• telescope diameter 15 cm
• launched 2003 June
• tracker lost 2006, but…
• still working better than ever
• 3” pixels, 1” pointing stability
• follow object up to 8 weeks
• time resolution ~sec-min
• 3 modes: Fabry (V = 0…6), direct
(V = 6…12), guide-star (<2006)
• CCD + B/V filter
Primary Science
• Asteroseismology  structure, age
• Exoplanets  sizes, atmospheres
Tony Moffat & the MOST team
Luminous Hot-star Highlights
• zeta Oph, O9.5Ve: Fig.1
• HD127756, B1/2Vne; HD217543, B3Vpe:
SPBe stars, 30-40 NRP g- (+ poss r-) modes,
excited by Fe opacity bump, v(rot) close to
break-up (Cameron et al. 2008).
• delta Ceti, B2IV: Fig.2.
• HD163899, B2Ib/II: Fig.3.
• HD 313926, B5: : largest eccentricity (e =
0.2) among short-period (3.5d) early-type
binaries  v. young (Rucinski et al. 2007).
• HD 163868, B5Ve: detection of ~60 modes,
first r-modes (v. low freq.) & g-modes (Fe
opacity bump) in a Be star  NRP important
in Be stars? (Walker et al. 2005).
• HD 163830, B5II/III: Fig.4.
• beta CMi, B8Ve: 1st detection of non-radial
(high-order) g-modes in a Be-star > B6 
pulsations excited in all classical Be stars?
Fe-bump @ 200kK, v(rot) ~ break-up, 3.5 M
(Saio et al. 2007).
• sigma Ori E, B2Vpe: being analyzed
(Townsend et al.).
• Rosette Nebula, 5 OB: to be analyzed.
• WR123, WN8: Fig.5.
• WR103, WC9d: Fig.6.
• WR111, WC5: Fig.7.
• WR110, WN5-6: being analyzed; P = 2.1d &
4.0d + stochastic?
• WR124, WN8h: being analyzed; P ~ 6d +
stochastic? Fig.8.
Fig.5: WR123, runaway, no H. P = 10h: 1st ~clear
pulsation period in a WR star  SMP driven by
normal Fe bump (Dorfi et al. 2006 – but took X(H) =
0.35) OR(?) g-modes driven by Fe bump at log T =
6.25 (Townsend & MacDonald 2006 – but took R =
2R cf. ~15 R observed). Spectral lines ~10% of
total broadband flux & vary little  observed variation
(P = 10h & other) must be related to pulsations of the
stellar core! (supported by sp analysis for WN8 stars
by Haeffener & Hamann 2008). Delayed reaction of
wind (sp lines) triggered by superposition of pulsation
events. Lefevre et al. (2005).
Fig1: zeta Oph: v sin i ~ 400 km/s, runaway;
clear beta Cep radial/NR pulsations driven by Fe
opacity bump (Walker et al. 2005).
Fig.2: delta Cep: Left: folded lc f1 = 6.2 c/d = 1st
radial overtone. Right: Fourier Sp after pre-whiten
(f1, 2f1)  multiperiodic (mono before). Models:
10.2 M, 18 Myr  evolved beta Cep star (Aerts
et al. 2006). N.B.: MOST’s first target!
Fig.4: HD 163830, a new
SPB (slowly-pulsating Bstar) with largest no. of
detected g-mode
frequencies; model  4.5
M (Aerts et al. 2006).
Fig.3: HD163899, ~35 frequencies: p- & gmode, latter 1st time in a BSG. Great potential
for asteroseismology (Saio et al. 2006).
Fig.7: WR111 (top) cf. WR123
(bottom) & WR103 (middle). No P
of A > 0.05 mmag (~40 x less cf.
SMP models: Glatzel et al. 1993)
for f = 10 – 1000 c/d (P = 1.4m –
2.4 h), after removing f = 14.2 c/d
MOST orbital + harmonics. Also:
no damped oscillations or flares
>~1 mmag. Moffat et al. (2007).
Fig.6: WR103, similar to WR123, except sl.
lower amplitude variations & no P. Both lightcurves = superposition of short-lived (5-7d
coherency), multiple-frequency pulsations
of amplitude 5-20 mmag mostly at freq.
<~1c/d. No periodic signal >0.2 mmag in
traditional domain freq. >~10 c/d. Moffat et
al. (2008).
Conclusions
Despite its modest size, MOST can provide powerful highprecision photometric constraints on the properties of hot
luminous stars. The key is contiguous coverage over long time
intervals from space.
Fig.8: HST H-alpha image of
M1-67 nebula around
WR124 (Grosdidier et al.
1998).