Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://star.arm.ac.uk/~csj/papers/posters/v652her5.ps Äàòà èçìåíåíèÿ: Mon Jul 1 16:08:32 2002 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 07:59:57 2012 Êîäèðîâêà:

Time-resolved spectral analysis of the pulsating helium star V652 Her
C.S. Jeery 1 , V.M.Woolf 1 and D.L.Pollacco 2
1. Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
2. School of Physical Sciences, Queen's University Belfast, Belfast BT7 9NN, N. Ireland
csj@star.arm.ac.uk, vmw@star.arm.ac.uk, D.Pollacco@qub.ac.uk
V652 Her
V652 Her is an early-type extreme helium star which
pulsates with a period of 0.108 days. Its surface com-
position and location in the HR diagram have posed
a considerable challenge to the theory of stellar evolu-
tion. However, its regular pulsation, a decreasing pul-
sation period and unusual surface composition have al-
lowed stringent tests of various evolution models. The
most successful model (Saio & Jeery 2000) involves
the merger of two helium white dwarfs which, after ex-
panding to become a yellow giant, contracts towards
the helium main sequence (where sdB stars are found).
The most poorly determined property of V652 Her is
its mass, a consequence of the diôculty of measuring
surface gravity. The most crucial measurement, how-
ever, is that of radius, which may be measured using
Baade's method. In this poster we summarise (bul-
leted highlights) the analysis of new observations (Jef-
fery et al. 2001) aimed at rening the radius and mass
measurements of V652 Her.
Observations
A series of 59 moderate-resolution high signal-to-noise
spectra of the pulsating helium star V652 Her covering
1.06 pulsation cycles were obtained with the William
Herschel Telescope in 1998 July. These have been
supplemented by archival ultraviolet and visual spec-
trophotometry and used to make a time-dependent
study of the properties of V652 Her throughout the
pulsation cycle.
Analysis
SFIT_SYNTH
STERNE
High resolution
spectrograms
UV + visual
spectrophotometry
Model flux grid Model structure grid
High resolution
model grid
v_t, composition
v_t
Atomic data
Teff, log g, v sin
composition
Teff, Eb-v
q
SPECTRUM
LTE_LINES
FFIT
SFIT
Figure 1. Block diagram illustrating the procedures
(boxes), inputs (ellipses) and outputs (oval boxes)
used in the analysis of high­resolution optical spec­
tra and broad­band spectrophotometry of V652 Her .
Figure 2. Radial veloc­
ity curve (top) with ccf
widths (middle) and the
residual arc shifts (bot­
tom). Note the small
velocity errors and the
ccf broadening at mini­
mum radius.
Figure 3. The run
of T eff , log g eff and
v sin i as a function of
phase as derived from
the high­resolution
spectra. The values of
v sin i represent the
formal solution from
the free­parameter fit.
Analysis of the new data features the following:
 new software for the automatic measurement of ef-
fective temperature, surface gravity and projected ro-
tation velocities from moderate-resolution spectra,
 the most precise radial velocity curve for V652 Her
measured so far,
 self-consistent high-precision measurements of ef-
fective temperature and surface gravity around the
pulsation cycle,
Figure 4. A sequence of line profiles for Si iii, He i,
He ii and other ions demonstrates line broadening
around minimum radius. Pulsation phase is shown
on the left. A single spectrum obtained around max­
imum radius ( = 0:633) is shown for comparison.
Rapid acceleration around minimum radius is visible
as a change from a red to a blue shift. The core of
He i 4713 š A broadens around phase 0.13.
 a demonstration of excessive line-broadening at
minimum radius and evidence for a pulsation-driven
shock front,
 a new method for the direct measurement of the
radius of a pulsating star using radial velocity and sur-
face gravity measurements alone,
Figure 5. Sections of the average normalized spec­
trum of near maximum radius (histogram) together
with the automatically computed best­fit synthetic
spectrum (smooth curve: T eff = 22 000 K; log g eff =
3:25(cgs); v t = 9 km s 1 ; v sin i = 7 km s 1 ).
 new software for the automatic measurement of
chemical abundances and microturbulent velocity,
 updated chemical abundances for V652 Her com-
pared with previous work (Jeery et al. 1999),
 a reanalysis of the total ux variations (cf. Lynas-
Gray et al. 1984) in good agreement with previous
work,
 an independent verication of the interstellar red-
dening using Lyman  from IUE high-resolution spec-
tra and spectrum synthesis.
Figure 6. UKIRT CGS4
J­band spectrum of
V652 Her showing
He i
(labelled by tran­
sition) and hydrogen
Paschen lines (P ; ô).
Figure 7. LTE
model spectrum
for V652 Her match­
ing the UKIRT J­band
spectrum.
 the rst infrared spectrum of an extreme helium
star, showing He 10830  A to be unexpectedly weak
and hydrogen Paschen lines to be unexpectedly strong
relative to other He i lines.
Figure 8. Derivation of radius from visual photometry
(Kilkenny & Lynas­Gray 1982: top panel). The angular
radius  is estimated by fitting model flux distributions
corresponding to the spectroscopic T eff to the visual
photometry (centre). The radius may be deduced from
the gradient of ô= 0 with ôr (bottom panel).
 revised measurements of the stellar mass and ra-
dius from a number of dierent diagnostics (surface
gravity, visual magnitude, bolometric ux).
The mass of V652 Her
Masses measured without reference to the ultraviolet
uxes turn out to be unphysically low ( 0:25M  ).
The best estimate for the dimensions of V652 Her av-
eraged over the pulsation cycle is given by:
 hT eff i = 22 930  10K
 hlog gi = 3:46  0:05 (ionization equilibrium),
 hT eff i = 20 950  70K (total ux method),
 hRi = 2:31  0:02R  ,
 hLi = 919  14L  ,
 M = 0:59  0:18M  and
 d = 1:70  0:02kpc.
Two signicant problems were encountered. The line-
blanketed hydrogen-decient model atmospheres used
yield eective temperatures from the optical spectrum
(ionization equilibrium) and visual and UV photome-
try (bolometric ux) that are inconsistent. Secondly,
the IUE spectra are poorly distributed in phase and
have low signal-to-noise. These problems may intro-
duce systematic errors of up to 0:1M  . New models
and new ultraviolet observations are required.
References
Jeery C.S., Hill P.W., Heber U., 1999. A&A 346, 491
Jeery C.S., Woolf V.M., Pollacco D., 2001. A&A in
press
Kilkenny D., Lynas-Gray A.E. 1982. MNRAS 198, 873
Lynas-Gray A.E., Schonberner D., Hill P.W., Heber
U., 1984. MNRAS 209, 387
Saio H., Jeery C.S., 2000. MNRAS 313, 671