Quantitative analysis of the V838 Monocerotis spectrum
We present the determination of the effective temperature, iron abundance, and microturbulent velocities for the pseudophotosphere of V838 Mon observed on February 25, March 2 and 26, 2002. Physical parameters of the line forming region were obtained in the framework of a self-consistent approach us...
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Головна астрономічна обсерваторія НАН України
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| Zitieren: | Quantitative analysis of the V838 Monocerotis spectrum / B. Kaminsky, Ya.V. Pavlenko // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 273-275. — Бібліогр.: 10 назв. — англ. |
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irk-123456789-796572015-04-04T03:02:32Z Quantitative analysis of the V838 Monocerotis spectrum Kaminsky, B. Pavlenko, Ya.V. MS3: Physics of Stars and Galaxies We present the determination of the effective temperature, iron abundance, and microturbulent velocities for the pseudophotosphere of V838 Mon observed on February 25, March 2 and 26, 2002. Physical parameters of the line forming region were obtained in the framework of a self-consistent approach using fits of synthetic spectra to observed spectra in the wavelength range 5500–6700 Å. We obtained the values of Teff 5330±150 K, 5540±150 K, and 4960±150 K for February 25, March 2, and March 26, 2002, respectively. The iron abundance logN(Fe) = −4.7 does not appear to change in the atmosphere of V838 Mon from February 25 to March 26, 2002. 2005 Article Quantitative analysis of the V838 Monocerotis spectrum / B. Kaminsky, Ya.V. Pavlenko // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 273-275. — Бібліогр.: 10 назв. — англ. 0233-7665 http://dspace.nbuv.gov.ua/handle/123456789/79657 en Кинематика и физика небесных тел Головна астрономічна обсерваторія НАН України |
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MS3: Physics of Stars and Galaxies MS3: Physics of Stars and Galaxies |
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MS3: Physics of Stars and Galaxies MS3: Physics of Stars and Galaxies Kaminsky, B. Pavlenko, Ya.V. Quantitative analysis of the V838 Monocerotis spectrum Кинематика и физика небесных тел |
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We present the determination of the effective temperature, iron abundance, and microturbulent velocities for the pseudophotosphere of V838 Mon observed on February 25, March 2 and 26, 2002. Physical parameters of the line forming region were obtained in the framework of a self-consistent approach using fits of synthetic spectra to observed spectra in the wavelength range 5500–6700 Å. We obtained the values of Teff 5330±150 K, 5540±150 K, and 4960±150 K for February 25, March 2, and March 26, 2002, respectively. The iron abundance logN(Fe) = −4.7 does not appear to change in the atmosphere of V838 Mon from February 25 to March 26, 2002. |
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Article |
| author |
Kaminsky, B. Pavlenko, Ya.V. |
| author_facet |
Kaminsky, B. Pavlenko, Ya.V. |
| author_sort |
Kaminsky, B. |
| title |
Quantitative analysis of the V838 Monocerotis spectrum |
| title_short |
Quantitative analysis of the V838 Monocerotis spectrum |
| title_full |
Quantitative analysis of the V838 Monocerotis spectrum |
| title_fullStr |
Quantitative analysis of the V838 Monocerotis spectrum |
| title_full_unstemmed |
Quantitative analysis of the V838 Monocerotis spectrum |
| title_sort |
quantitative analysis of the v838 monocerotis spectrum |
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Головна астрономічна обсерваторія НАН України |
| publishDate |
2005 |
| topic_facet |
MS3: Physics of Stars and Galaxies |
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http://dspace.nbuv.gov.ua/handle/123456789/79657 |
| citation_txt |
Quantitative analysis of the V838 Monocerotis spectrum / B. Kaminsky, Ya.V. Pavlenko // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 273-275. — Бібліогр.: 10 назв. — англ. |
| series |
Кинематика и физика небесных тел |
| work_keys_str_mv |
AT kaminskyb quantitativeanalysisofthev838monocerotisspectrum AT pavlenkoyav quantitativeanalysisofthev838monocerotisspectrum |
| first_indexed |
2025-07-06T03:40:53Z |
| last_indexed |
2025-07-06T03:40:53Z |
| _version_ |
1836867391391268864 |
| fulltext |
QUANTITATIVE ANALYSIS OF THE V838 MONOCEROTIS SPECTRUM
B. Kaminsky, Ya. V. Pavlenko
Main Astronomical Observatory, NAS of Ukraine
27 Akademika Zabolotnoho Str., 03680 Kyiv, Ukraine
e-mail: bogdan@mao.kiev.ua
We present the determination of the effective temperature, iron abundance, and microturbulent
velocities for the pseudophotosphere of V838 Mon observed on February 25, March 2 and 26, 2002.
Physical parameters of the line forming region were obtained in the framework of a self-consistent
approach using fits of synthetic spectra to observed spectra in the wavelength range 5500–6700 Å.
We obtained the values of Teff 5330± 150 K, 5540± 150 K, and 4960± 150 K for February 25,
March 2, and March 26, 2002, respectively. The iron abundance log N(Fe) = −4.7 does not appear
to change in the atmosphere of V838 Mon from February 25 to March 26, 2002.
INTRODUCTION
The peculiar variable star V838 Mon was discovered during an outburst of the beginning of January 2002 [1].
Two further outbursts were then observed in February 2002 [2, 8]; in general, the visual magnitude of the star
increased by 9 mag. The spectral evolution was dramatic — from an A-type star with many emission P Cyg
lines at the time of the first outburst to a G–K giant in February–March 2002 [5] and, finally, to a L-supergiant
in October 2002 [3].
The outburst mechanism as well the nature of progenitor of V838 Mon remain a mystery.
OBSERVATIONS
We used three echelle spectra — a first one (from February 25) was observed during the period between
the second and third outbursts, and the two (from March 2 and 26) — after the third outburst. This spectra
was kindly provided for us by Drs. Ulisse Munary (February 25 and March 26; R =18 000; freely available from
[http://ulisse.pd.astro.it/V838Mon/]) and Lisa Crause (March 2; R =36 000) — see more details in [2]
and [8].
PROCEDURE
Our synthetic spectra were computed in the framework of the classical approach: LTE, plane-parallel media,
no sinks and sources of energy inside the atmosphere. Strictly speaking, none of these assumption is 100% valid
in atmosphere of V838 Mon.
We computed a sample of LTE synthetic spectra for a grid of the Kurucz model atmospheres [7] with
Teff = 4000÷ 6000 K using the WITA612 program [9]. Synthetic spectra were computed with a wavelength step
of 0.02 Å, microturbulent velocities of 2÷ 18 km s−1 with a step 1 km s−1, iron abundances log N(Fe) = −5.6 →
−3.6 dex1 with a step of 0.1 dex. Then, due to the high luminosity of the star, we formally adopt log g =0.
Synthetic spectra were computed for the VALD line list [6]. The computed synthetic spectra were convolved
with different profiles, and then fitted to the observed spectra following the numerical scheme described in [4, 10].
RESULTS
The example of obtained best fits of the synthetic spectra to the observed spectrum of V838 Mon for February 25
is shown in Fig. 1. The plot shows the fits for: (a) “the best” Teff , and (b) an effective temperature, which
has been reduced by 1000 K. This last value corresponds better with the Teff obtained from photometric
measurements (cf. [8]).
Results of the determination of atmospheric parameters of V838 Mon in February and March 2002 are given
in Table 1. In Table 1 Vt is a microturbulent velocity, Vg is a parameter of macroturbulence and Vr is a radial
velocity.
c© B. Kaminsky, Ya. V. Pavlenko, 2004
1 In the paper we use the abundance scale
∑
Ni = 1.
273
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
5500 5520 5540 5560 5580 5600 5620 5640 5660 5680
N
or
m
al
is
ed
F
lu
x
Wavelength (Å)
V 838 Mon
Teff=5750 K
Teff=4500 K
Figure 1. The best fits of synthetic spectra to the observed spectrum of V838 Mon on February 25, 2002, obtained by
the minimization procedure
CONCLUSIONS
• The effective temperature for the most last date (March 26) is somewhat lower than for the previous
dates. This is an expected result, taking into account an gradual cooling of the envelope.
• For March 2 we obtained a slightly higher value of the temperature than for February 25. A possible
explanation is the heating of the pseudophotosphere as result of the third outburst which occurred before
March 2.
• Our deduced “effective temperatures” as well as Teff derived in [5] for all dates do not correspond with
values obtained from the photometry (Teff ∼ 4200–4500 K). Most probably, the line-forming region is
heated by supersonic motions — the formally determined microturbulent velocity Vt = 13 km s−1 exceeds
the sound velocity in the atmosphere (4–5 km s−1).
• We obtained a moderate deficit of iron logN(Fe) ∼ -4.7 in the atmosphere of V838 Mon, and we do
not see any significant change in the iron abundance from February 25 to March 26. In [5] was derived
logN(Fe)∼ –4.9 for March 18.
• The microturbulent velocities (Vt ∼ 13 km s−1) are very similar and extremely high for all three dates.
This value also agree with a value Vt = 12 km s−1 obtained in [5].
• Analysis shows a lower value of Vg for the later dates: the effects of expansion and macroturbulence were
weakened at the later stages of the evolution of the pseudophotosphere of V838 Mon.
Table 1. Atmospheric parameters for V838 Mon
Date Teff Vt (km s−1) log N(Fe) Vg (km s−1) Vr (km s−1)
February 25 5330 13.2 −4.73 54.7 −76.5
March 2 5540 13.3 −4.75 47.8 −77.6
March 26 4960 12.5 −4.68 42.5 −65.2
274
We stress once again that the used static LTE model is very sketchy for this star and, therefore, most of our
results are rather qualitative, and they should be confirmed and/or refined in the future.
Acknowledgements. We thank Drs. Ulisse Munari, Lisa Crause for providing spectra and for discussions of
our results. This research was partially supported by a PPARC visitors grants from PPARC and the Royal
Society. Y. P.’s studies are partially supported by a Small Research Grant from the American Astronomical
Society.
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Notic. Roy. Astron. Soc.–2003.–341.–P. 785–791.
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[4] Jones H. R. A., Pavlenko Ya., Viti S., Tennyson J. Spectral analysis of water vapour in cool stars // Mon. Notic.
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[7] Kurucz R. L. CDROM 23, Harvard–Smithsonian Observatory, 1993.
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