X-ray and molecular emission from the nearest region of recent star formation

Science

Volumn 277, Issue 5322, 1997, Pages 67-71

  Kastner, J H ^a   Zuckerman, B ^b   Weintraub, D A ^c   Forveille, T ^d  

^a MASSACHUSETTS INSTITUTE OF TECHNOLOGY   (United States)

^b UNIVERSITY OF CALIFORNIA   (United States)

^c VANDERBILT UNIVERSITY   (United States)

^d OBSERVATOIRE DE GRENOBLE   (France)

Author keywords

[No Author keywords available]

Indexed keywords

CARBON MONOXIDE; CYANIDE; HYDROGEN CYANIDE;

ARTICLE; ASTRONOMY; INFRARED RADIATION; PRIORITY JOURNAL; X RAY;

ASTRONOMY; CARBON MONOXIDE; CYANIDES; EVOLUTION, PLANETARY; EXTRATERRESTRIAL ENVIRONMENT; FORMATES; HYDROGEN CYANIDE; SPECTROMETRY, X-RAY EMISSION; SPECTRUM ANALYSIS; X-RAYS;

EID: 0030803191     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.277.5322.67     Document Type: Article

References (43)

1. S. M. Rucinski and J. Krautter, Astron. Astrophys. 121, 217 (1983).
2. R. de la Reza, C. A. O. Torres, G. Quast, B. V. Castilho, G. L. Vieira, Astrophys. J. 343, L61 (1989).
3. The combination of Hα emission and strong Li absorption indicates stellar youth and is commonly used to identify T Tauri stars. The strength of the Hα emission serves to classify such stars either as classical (commonly defined as a T Tauri star with an Hα emission equivalent width of ≥10 Å) or weak-lined.
4. D. A. Weintraub, G. Sandell, W. Duncan, Astrophys. J. 340, L69 (1989).
5. E. D. Feigelson, ibid. 468, 306 (1996).
6. J. Gregorio-Metern, J. R. D. Lepine, C. A. O. Torres, R. de la Reza, Astron. J. 103, 549 (1992).
7. B. Zuckerman, T. Forveille, J. H. Kastner, Nature 373, 494 (1995).
8. Hen(3) 600 and CoD -33° 7795 might be considered classical T Tauri stars on the basis of Hα emission alone. However, some authors also use the presence of excess near-IR emission to discriminate between classical and weak-lined T Tauri stars. Extrapolating from existing photometry, we anticipate that CoD -33° 7795 does not have a near-IR excess and therefore is likely to be better classified as weaklined. The near-IR flux of Hen 600 is more difficult to predict, and its status (weak-lined versus classical) remains uncertain.
9. R. Neuhaueser, M. F. Sterzik, J. H. M. M. Schmitt, R. Wichmann, J. Krautter, Astron. Astrophys. 297, 391 (1995).
10. W. A. Lawson, E. D. Feigelson, D. P. Huenemoerder, Mon. Not. R. Astron. Soc. 280, 1071 (1996).
11. S. Casanova, T. Montmerle, E. D. Feigelson, P. André, Astrophys. J. 439, 752 (1995).
12. E. D. Feigelson, S. Casanova,T. Montmerle, J. Guibert, ibid. 416, 623 (1993).
13. W. Voges et al., Astron. Astrophys., in press.
14. J. R. Stauffer, J.-P. Caillault, M. Gagné, C. F. Prosser, L. W. Hartmann, Astrophys. J. Suppl. Ser. 91, 625 (1994).
15. S, Randich, J. H. M. M. Schmitt, C. F. Prosser, J. R. Stauffer, Astron. Astrophys. 300, 134 (1995).
16. _, ibid. 305, 785 (1996).
17. B. M. Patten and T. S. Simon, Astrophys. J. Suppl. Ser. 106, 489 (1996).
18. J. P. Pye, S. T. Hodgkin, R. A. Stern, J. R. Stauffer, Mon. Not. R. Astron. Soc. 266, 798 (1994).
19. bol) ∼-3(74). This would appear to represent the maximum efficiency with which dynamo activity (resulting from the combination of fast rotation and deep convection) can convert a star's luminosity to coronal x-ray emission. Subsequently, single low-mass stars gradually spin down and become less active; by the time such stars are as old as the sun, they are relatively meager x-ray emitters.
20. bol) ∼-3(74). This would appear to represent the maximum efficiency with which dynamo activity (resulting from the combination of fast rotation and deep convection) can convert a star's luminosity to coronal x-ray emission. Subsequently, single low-mass stars gradually spin down and become less active; by the time such stars are as old as the sun, they are relatively meager x-ray emitters.
21. The presence and strength of Li absorption in the spectrum of a young star are useful, but controversial age indicators [see discussion in (32)]. Models predict that Li should be fully depleted in stars of the mass of TW Hya by ∼10 My (22); however, substantial abundances of Li are present in low-mass stars that are as old as 30 to 100 My [J. R. Stauffer et al., Astrophys. J. 479, 776 (1997); M. Zboril et al., Mon. Not. R Astron. Soc. 284, 685 (1997)].
22. The presence and strength of Li absorption in the spectrum of a young star are useful, but controversial age indicators [see discussion in (32)]. Models predict that Li should be fully depleted in stars of the mass of TW Hya by ∼10 My (22); however, substantial abundances of Li are present in low-mass stars that are as old as 30 to 100 My [J. R. Stauffer et al., Astrophys. J. 479, 776 (1997); M. Zboril et al., Mon. Not. R Astron. Soc. 284, 685 (1997)].
23. S. Stahler, personal communication.
24. F. D'Antona and I. Mazzitelli, Astrophys. J. Suppl. Ser. 90, 467 (1994).
25. After this paper was accepted, we became aware of the Hipparcos satellite parallax measurements of the distances to TW Hya, 56 ± 7 pc (R. Wichmann, U. Bastian, J. Krautter, I. Jankovics, S. M. Rucinski, paper presented at the Hipparcos Venice '97 Symposium, Venice, Italy, 13 to 16 May 1997), and HD98800, 47 ± 6 pc [from data available in the Hipparcos catalog (http://vizier.u-strasbg.fr/cgi-bin/ VizieR) as of 17 June 1997]. These distances agree with our estimates (Table 1) and confirm our earlier conclusions.
26. L. Magnani, J.-P. Caillault, A. Buchalter, C. A. Beichmann, Astrophys. J. Suppl. Ser. 96, 1 (1995).
27. A. Ghez, personal communication.
28. We used receivers A2, B3i, and C2 for measurements in the 230-, 345-, and 460-GHz atmospheric windows. Beam sizes at these frequencies were 20″, 14″, and 11″, respectively. The back end was the JCMT Digital Autocorrelation Spectrometer (DAS); we used a DAS bandwidth of 250 MHz, which yields a spectral resolution of 189 kHz. We obtained data by switching the secondary mirror at 1 Hz between the position of TW Hya and a nearby reference position located 60″ away (40″ away, for observations at 460 GHz). Typical total integration times were on the order of 1 hour. To convert from antenna temperatures to brightness temperatures, we applied aperture efficiencies of 0.57, 0.49, and 0.31 for observations in the 230-, 345-, and 460-GHz windows, respectively.
29. CO). Such a density is sufficient to excite the (3-2) and (4-3) transitions of HCN [R. Genzel, in Millimeter and Submillimeter Astronomy, R. D. Wolstencroft and W. B. Burton, Eds. (Kluwer, Norwell, MA, 1987), p. 223].
30. S. V. W. Beckwith and A. I. Sargent, Astrophys. J. 402, 280 (1993); T. Omodaka, Y. Kitamura, E. Kawazoe, ibid. 396, 187 (1992).
31. S. V. W. Beckwith and A. I. Sargent, Astrophys. J. 402, 280 (1993); T. Omodaka, Y. Kitamura, E. Kawazoe, ibid. 396, 187 (1992).
32. S. Rucinski, Astron. J. 90, 2321 (1985).
33. P. Cox, A. Omont, P. J. Huggins, R. Bachiller, T. Forveille, Astron. Astrophys. 266, 420 (1992); R. Bachiller, T. Forveille, P. J. Huggins, P. Cox, ibid., in press.
34. P. Cox, A. Omont, P. J. Huggins, R. Bachiller, T. Forveille, Astron. Astrophys. 266, 420 (1992); R. Bachiller, T. Forveille, P. J. Huggins, P. Cox, ibid., in press.
35. S. V. W. Beckwith, A. I. Sargent, R. S. Chini, R. Gusten, Astron. J. 99, 924 (1990).
36. D. R. Soderblom, T. J. Henry, M. D. Shetrone, B. F. Jones, S. H. Saar, Astrophys. J. 460, 984 (1996).
37. G. Torres, R. P. Stefanik, D. W. Latham, T. Mazeh, ibid. 452, 870 (1995).
38. J. H. Kastner, unpublished data.
39. Our criteria for selecting stars in the range of spectral types K5 to M3 were published spectral type or stellar effective temperature or B-V and V-I colors (or both) (where we adopted ranges of B-V between 1.1 and 1.6 and V-I between 1.6 and 2.9).
40. ex.
41. A. Dutrey, S. Guilloteau, M. Guelin, Astron. Astrophys. Lett. 317, L55 (1997).
42. T. A. Fleming. J. H. M. M. Schmitt, W. A. Giampapa, Astrophys. J. 450, 401 (1995).
43. J.H.K.'s research at the Massachusetts Institute of Technology was supported in part by the Advanced X-ray Astrophysics Facility Science Center as part of Smithsonian Astrophysical Observatory contract SVI-61010 under the NASA Marshall Space Flight Center. Additional support was provided by NASA Origins of Solar Systems program grants (NAGW 5020 and 5145) to Vanderbilt University (D.A.W.) and by an NSF grant (AST-9417158) to the University of California, Los Angeles (B.Z.). We thank E. J. Gaidos (M.I.T.) and H. Matthews (Joint Astronomy Centre), who assisted in the molecular line observations, and T. S. Simon, who provided data before publication. Our molecular abundance calculations made use of the Jet Propulsion Laboratory's online Molecular Spectroscopy database.