2008A&A...484..225M


Query : 2008A&A...484..225M

2008A&A...484..225M - Astronomy and Astrophysics, volume 484, 225-239 (2008/6-2)

Molecular hydrogen in the circumstellar environments of Herbig Ae/Be stars probed by FUSE.

MARTIN-ZAIEDI C., DELEUIL M., LE BOURLOT J., BOURET J.-C., ROBERGE A., DULLEMOND C.P., TESTI L., FELDMAN P.D., LECAVELIER DES ETANGS A. and VIDAL-MADJAR A.

Abstract (from CDS):

Molecular hydrogen (H2) gas is the most abundant molecule in the circumstellar (CS) environments of young stars. It is thus a key element in our understanding of the evolution of pre-main sequence stars and their environments towards the main sequence. At the present time, little is known about the gas as compared to the dust in the environments of young stars. We thus observed molecular hydrogen around a sample of pre-main sequence stars in order to better characterize their gaseous CS environments. The FUSE (Far Ultraviolet Spectroscopic Explorer) spectral range offers access to electronic transitions of H2. We analyzed the FUSE spectra of a sample of Herbig Ae/Be stars (HAeBes) covering a broad spectral range (from F4 to B2), including the main-sequence A5 star β Pictoris. To better diagnose the origin of the detected molecular gas and its excitation conditions, we used a model of a photodissociation region. Our analysis demonstrates that the excitation of H2 is clearly different around most of the HAeBes compared to the interstellar medium. Moreover, the characteristics of H2 around Herbig Ae and Be stars give evidence for different excitation mechanisms. For the most massive stars of our sample (B8 to B2 type), the excitation diagrams are reproduced well by a model of photodissociation regions (PDR). Our results favor an interpretation in terms of large CS envelopes, remnants of the molecular clouds in which the stars were formed. On the other hand, the group of Ae stars (later than B9 type) known to possess disks is more inhomogeneous. In most cases, when CS H2 is detected, the lines of sight do not pass through the disks. The excitation conditions of H2 around Ae stars cannot be reproduced by PDR models and correspond to warm and/or hot excited media very close to the stars. In addition, no clear correlation has been found between the ages of the stars and the amount of circumstellar H2. Our results suggest structural differences between Herbig Ae and Be star environments. Herbig Be stars do evolve faster than Ae stars, and consequently, most Herbig Be stars are younger than Ae ones at the time we observe them. It is thus more likely to find remnants of their parent cloud around them.

Abstract Copyright:

Journal keyword(s): stars: circumstellar matter - stars: formation - stars: pre-main sequence - ISM: molecules

Simbad objects: 24

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Number of rows : 24
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 LDN 1521D DNe 04 27 46.5 +26 18 52           ~ 215 0
2 V* HK Tau TT* 04 31 50.5715875272 +24 24 17.775307548 16.81 16.689 15.292     M0.5 319 1
3 V* GM Aur Or* 04 55 10.9815576936 +30 21 59.373771876 14.59 13.351 12.242 11.798   K3Ve 615 0
4 V* AB Aur Ae* 04 55 45.8458932216 +30 33 04.292077032 7.20 7.16 7.05 6.96 6.70 A0Ve 992 2
5 HD 36112 Ae* 05 30 27.5285630040 +25 19 57.076288752   8.57 8.27     A8Ve 416 0
6 NGC 2024 Cl* 05 41 43 -01 50.5           ~ 1108 1
7 HD 38087 ** 05 43 00.5754723576 -02 18 45.389406240 7.96 8.40 8.29 8.06 7.89 B3II 157 1
8 * bet Pic PM* 05 47 17.0876901 -51 03 59.441135 4.13 4.03 3.86 3.74 3.58 A6V 1781 1
9 HD 250550 Ae* 06 01 59.9892055464 +16 30 56.727549864   9.60 9.593 9.64   B9e 238 1
10 HD 259431 Ae* 06 33 05.1906369144 +10 19 19.982565336 8.39 8.95 8.72     B6ep 275 1
11 CD-44 3318 Ae* 07 19 28.2886716751 -44 35 11.235575735   10.47 9.99     A1e/F2IIIe 120 0
12 HD 76534 Be* 08 55 08.70673 -43 27 59.8852 7.04 7.62 7.50 8.94   B2Vn 120 0
13 HD 85567 Be* 09 50 28.5375988920 -60 58 02.954048268 8.16 8.67 8.57     B5Vne 86 0
14 V* TW Hya TT* 11 01 51.9053285064 -34 42 17.033218380   11.94 10.50 10.626 9.18 K6Ve 1735 1
15 HD 97048 Ae* 11 08 03.3109731720 -77 39 17.490777444 9.03 8.76 9.00   8.64 A0Vep 497 0
16 HD 100453 Ae* 11 33 05.5766482920 -54 19 28.547100696   8.09 7.79     A9Ve 242 1
17 HD 100546 Be* 11 33 25.4408872296 -70 11 41.241297948   6.71 6.30   6.64 A0VaekB8_lB 717 1
18 V* DX Cha Ae* 12 00 05.0868602544 -78 11 34.565724312   6.81 6.60     A0_sh 321 0
19 HD 109573 PM* 12 36 01.0317461592 -39 52 10.220465388   5.786 5.774 7.25 5.81 A0V 589 1
20 HD 135344 * 15 15 48.9462675744 -37 08 55.731368400   7.84 7.76     A0V 136 1
21 HD 141569 Y*O 15 49 57.7482550392 -03 55 16.341617064 7.22 7.20 7.12 7.00 7.04 A2VekB9mB9(_lB) 500 0
22 LDN 183 MoC 15 54 12.2 -02 49 42           ~ 724 1
23 HD 163296 Ae* 17 56 21.2881851168 -21 57 21.871819008 7.00 6.93 6.85 6.86 6.67 A1Vep 953 0
24 HD 176386 Y*O 19 01 38.9318002416 -36 53 26.561166432 7.28 7.44 7.32 8.11   B9V 124 0

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2022.05.20-23:05:12

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