CrH and FeH bands in atmospheres of the ultracool objects
Absorption CrH and FeH bands are of importance for study of atmospheres of ultracool dwarfs (Teff < 2200 K). Results from calculations of synthetic spectra of these objects using the new theoretical CrH and FeH opacities obtained by Burrows et al. [2] and Dulick et al. [3], respectively, are disc...
Збережено в:
| Дата: | 2005 |
|---|---|
| Автори: | , |
| Формат: | Стаття |
| Мова: | English |
| Опубліковано: |
Головна астрономічна обсерваторія НАН України
2005
|
| Назва видання: | Кинематика и физика небесных тел |
| Теми: | |
| Онлайн доступ: | http://dspace.nbuv.gov.ua/handle/123456789/79656 |
| Теги: |
Додати тег
Немає тегів, Будьте першим, хто поставить тег для цього запису!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | CrH and FeH bands in atmospheres of the ultracool objects / S. Zhukovska, Ya.V. Pavlenko // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 270-272. — Бібліогр.: 6 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-79656 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-796562015-04-04T03:02:25Z CrH and FeH bands in atmospheres of the ultracool objects Zhukovska, S. Pavlenko, Ya.V. MS3: Physics of Stars and Galaxies Absorption CrH and FeH bands are of importance for study of atmospheres of ultracool dwarfs (Teff < 2200 K). Results from calculations of synthetic spectra of these objects using the new theoretical CrH and FeH opacities obtained by Burrows et al. [2] and Dulick et al. [3], respectively, are discussed. Comparison of the CrH and FeH spectra computed with the JOLA approximation and Burrows data is carried out. Dependencies of SEDs of ulracool dwarfs on temperature, gravity, dust opacity are discussed. We compare our synthetic SEDs with an observed spectrum of Kelu-1 (L2). 2005 Article CrH and FeH bands in atmospheres of the ultracool objects / S. Zhukovska, Ya.V. Pavlenko // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 270-272. — Бібліогр.: 6 назв. — англ. 0233-7665 http://dspace.nbuv.gov.ua/handle/123456789/79656 en Кинематика и физика небесных тел Головна астрономічна обсерваторія НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
MS3: Physics of Stars and Galaxies MS3: Physics of Stars and Galaxies |
| spellingShingle |
MS3: Physics of Stars and Galaxies MS3: Physics of Stars and Galaxies Zhukovska, S. Pavlenko, Ya.V. CrH and FeH bands in atmospheres of the ultracool objects Кинематика и физика небесных тел |
| description |
Absorption CrH and FeH bands are of importance for study of atmospheres of ultracool dwarfs (Teff < 2200 K). Results from calculations of synthetic spectra of these objects using the new theoretical CrH and FeH opacities obtained by Burrows et al. [2] and Dulick et al. [3], respectively, are discussed. Comparison of the CrH and FeH spectra computed with the JOLA approximation and Burrows data is carried out. Dependencies of SEDs of ulracool dwarfs on temperature, gravity, dust opacity are discussed. We compare our synthetic SEDs with an observed spectrum of Kelu-1 (L2). |
| format |
Article |
| author |
Zhukovska, S. Pavlenko, Ya.V. |
| author_facet |
Zhukovska, S. Pavlenko, Ya.V. |
| author_sort |
Zhukovska, S. |
| title |
CrH and FeH bands in atmospheres of the ultracool objects |
| title_short |
CrH and FeH bands in atmospheres of the ultracool objects |
| title_full |
CrH and FeH bands in atmospheres of the ultracool objects |
| title_fullStr |
CrH and FeH bands in atmospheres of the ultracool objects |
| title_full_unstemmed |
CrH and FeH bands in atmospheres of the ultracool objects |
| title_sort |
crh and feh bands in atmospheres of the ultracool objects |
| publisher |
Головна астрономічна обсерваторія НАН України |
| publishDate |
2005 |
| topic_facet |
MS3: Physics of Stars and Galaxies |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/79656 |
| citation_txt |
CrH and FeH bands in atmospheres of the ultracool objects / S. Zhukovska, Ya.V. Pavlenko // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 270-272. — Бібліогр.: 6 назв. — англ. |
| series |
Кинематика и физика небесных тел |
| work_keys_str_mv |
AT zhukovskas crhandfehbandsinatmospheresoftheultracoolobjects AT pavlenkoyav crhandfehbandsinatmospheresoftheultracoolobjects |
| first_indexed |
2025-07-06T03:40:50Z |
| last_indexed |
2025-07-06T03:40:50Z |
| _version_ |
1836867388636659712 |
| fulltext |
CrH AND FeH BANDS IN ATMOSPHERES
OF THE ULTRACOOL OBJECTS
S. Zhukovska, Ya. V. Pavlenko
Main Astronomical Observatory, NAS of Ukraine
27 Akademika Zabolotnoho Str., 03680 Kyiv, Ukraine
e-mail: sveta@mao.kiev.ua, yp@mao.kiev.ua
Absorption CrH and FeH bands are of importance for study of atmospheres of ultracool dwarfs
(Teff < 2200 K). Results from calculations of synthetic spectra of these objects using the new
theoretical CrH and FeH opacities obtained by Burrows et al. [2] and Dulick et al. [3], respectively,
are discussed. Comparison of the CrH and FeH spectra computed with the JOLA approxima-
tion and Burrows data is carried out. Dependencies of SEDs of ulracool dwarfs on temperature,
gravity, dust opacity are discussed. We compare our synthetic SEDs with an observed spectrum
of Kelu-1 (L2).
INTRODUCTION
In this paper we deal with the opacities provided by hydrides CrH and FeH in atmospheres of ultracool dwarfs.
Due to low temperatures and high pressures in the atmospheres, Ti and V atoms are bonded into grains.
The CrH and FeH molecular bands play more important roles in spectra of ultracool dwarfs, they are the main
sources of the opacity in atmospheres of L-dwarfs near λ= 1 mkm. In particular, the 0–0 and 1–0 bands of
the CrH A6Σ+−X6Σ+ transition are used as primary markers for a new L-dwarf spectral class. First numerical
studies of the CrH A6Σ+−X6Σ+ transition were based on the raw CrH band data, but they allowed to estimate
such for this transition important parameters as the oscillator strengths [4]. For the FeH molecules oscillator
strengths were to be estimated too. Detailed studies of the CrH and FeH bands were impossible without
an precise line list. Recently, ab initio calculations of the CrH and FeH line positions and strengths were made
by Burrows et al. [2] and by Dulick et al. [3], respectively. We use them by analysis of molecular bands of these
species in spectra of ultracool dwarfs.
PROCEDURE
Considering the chemical equilibrium of more than 100 species in the LTE, we compute the theoretical spectra
using a version of the WITA program developed by Pavlenko [5]. We use the DUSTY and COND model
atmospheres calculated by Allard [1] for two limited cases of the dust formation: an inefficient gravitational
settling (dust depletes refractory elements and affects the thermal structure of the atmosphere) and an efficient
settling (dust affect only the depletion of the gas). To compare our SEDs with observations we include the opacity
of a dust cloud with a certain thickness which is located at a given depth in the atmosphere. Then, we assume
that extended profiles of the K I and Na I resonance lines can be described by the Voight profile.
RESULTS
• Results of calculations for CrH and FeH molecules are presented in Fig. 1, which shows the SEDs computed
taking into account the only molecular source of the opacity – CrH, FeH or TiO molecules in the DUSTY
model 18/5.0/0.0. For comparison, a TiO spectrum is also presented here, since TiO molecules are one of
the main sources of the opacity in atmospheres of M-dwarfs.
• Dependence of the density ratio of CrH and FeH molecules on the effective temperature and surface gravity
of a model atmosphere is studied. In Fig. 2 the density ratio of CrH and FeH molecules versus the gas
pressure is presented for a set of model atmospheres. At the left-hand panel one can see the dependence
of n[CrH]/n[FeH] on the temperature, on the right-hand panel – on the surface gravity of the atmosphere.
We show here differences between results obtained for the COND and DUSTY models.
c© S. Zhukovska, Ya. V. Pavlenko, 2004
270
0
4
8
12
16
20
7000 8000 9000 10000 11000 12000 13000
F
λ+
C
λ (Α)
CrH+alkali metals
FeH+alkali metals
TiO+alkali metals
Figure 1. Synthetic spectra calculated by taking into account the TiO, CrH or FeH opacity using the DUSTY model
18/5.0/0.0. The thin solid curve shows the continuum
10-1
100
101
102
103
104
105
101 102 103 104 105 106 107 108
n
(
C
r
H
)
/
n
(
F
e
H
)
Pg (dyn/cm
2)
DUSTY 18-5.0-0.0
DUSTY 24-5.0-0.0
COND 18-5.0-0.0
COND 24-5.0-0.0
10-1
100
101
102
103
100 101 102 103 104 105 106 107 108 109
n
(
C
r
H
)
/
n
(
F
e
H
)
Pg (dyn/cm
2)
DUSTY 24-4.0-0.0
DUSTY 24-6.0-0.0
DUSTY 18-6.0-0.0
a) b)
Figure 2. Dependence of the concentration ratio n[CrH]/n[FeH] on the temperature (a) and gravity (b)
0
1
2
3
4
5
6
7500 8000 8500 9000 9500 10000 10500 11000
F
λ+
C
λ (Α)
BURROWS
JOLA
Figure 3. Comparison of a synthetic spectrum obtained with the use of the DUSTY model 18/5.0/0.0 and the JOLA
approximation with the Burrows’s calculations for CrH molecule
271
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
8500 9000 9500 10000 10500 11000 11500 12000 12500
F
λ+
C
λ (Α)
Kelu-1
COND 22-4.5-0.0 A1.005.n2
Figure 4. Comparison of a synthetic spectrum for the COND model 22–4.5–0.0 with an observed spectrum of the L-dwarf
Kelu-1 [6]. For the calculations the opacity of a dust cloud with the optical thickness τtot = 1 at the depth τ = 0.005 is
used
• We compare synthetic spectra computed with the Burrows data and with the JOLA approximation that
were used in the first analysis of the CrH bands in atmospheres of L-dwarf [4]. As shown in Fig. 3 the JOLA
approximation describes the main spectrum features near 760 nm and 870 nm quite well. This proves
that the molecule oscillator strengths of the CrH A6Σ+ − X6Σ+ transition estimated by Pavlenko [4] –
gf = 0.006 ÷ 0.012 – are very close to the precise ones.
• To compare our results with observed spectra we computed the SEDs taking into account the opacity of
dust clouds with various parameters. In Fig. 4 we present an observed spectrum of the L-dwarf Kelu-1 and
a synthetic spectrum calculated for a dust cloud with the optical thickness τtot = 1 located at the depth
τ = 0.005; the COND model atmosphere 22–4.5–0.0 is used.
Acknowledgements. We are grateful to A. Burrow and M. Dulick for the CrH and FeH line lists in a digital
form. F. Allard is to be thanked for the model atmospheres of cool stars. We thank S. Legett for the observed
spectrum of the L-dwarf Kelu-1.
[1] Allard F. Model Atmospheres and Spectra of Brown Dwarfs to Giant Planets // From Giant Planets to Cool
Stars.–2000.–212.–P. 127.
[2] Burrows A., Ram R. S., Bernath P. New CrH Opacities for the Study of L and Brown Dwarf Atmospheres //
Astrophys. J.–2002.–577.–P. 986–992.
[3] Dulick M., Bauschlincher C. W., Burrows A. Line intensities and molecular opacities of the FeH F 4Δi − X4Δi
transition // Astrophys. J.–2003.–594.–P. 651–663.
[4] Pavlenko Ya. V. CrH Molecular Bands in the Spectra of Late-Type Dwarfs // Astron. J.–1999.–76, N 10.–
P. 847–852.
[5] Pavlenko Ya. V. Lithium Lines in the Spectra of M Dwarfs: UX Tau C // Astron. Rep.–2000.–44.–P. 219.
[6] Ruiz M. T., Leggett S. K., Allard F. Kelu-1: A Free-floating Brown Dwarf in the Solar Neighborhood // Astrophys.
J.–1997.–491.–P. L107–L110.
272
|