Optical observations of comet Hale-Bopp (C/1995 O1) at large heliocentric distances before perihelion.

[en] The activity of comet Hale-Bopp (C/1995 O1) was monitored monthly by optical imaging and long-slit spectroscopy of its dust and gas distribution over heliocentric distances of 4.6 to 2.9 AU. The observed band intensities of the NH[SUB]2[/SUB] radical and the H[SUB]2[/SUB]O[SUP]+[/SUP] ion cannot be explained by existing models of fluorescence excitation, warranting a reexamination of the corresponding production rates, at least at large heliocentric distances. Comparing the production rate of the CN radical to its proposed parent, HCN, shows no evidence for the need of a major additional source for CN in Hale-Bopp at large heliocentric distances. The dust and CN production rates are consistent with a significant amount of sublimation occurring from icy dust grains surrounding Hale-Bopp.

Disciplines :

Space science, astronomy & astrophysics

Author, co-author :

Rauer, H.

Arpigny, Claude ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)

Boehnhardt, H.

Colas, F.

Crovisier, J.

Jorda, L.

Kuppers

Manfroid, Jean ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)

Rembor, K.

Thomaa

Language :

English

Title :

Optical observations of comet Hale-Bopp (C/1995 O1) at large heliocentric distances before perihelion.

Publication date :

01 March 1997

Journal title :

Science

ISSN :

0036-8075

eISSN :

1095-9203

Publisher :

American Association for the Advancement of Science, Washington, United States - District of Columbia

Volume :

275

Pages :

1909-1912

Peer reviewed :

Peer Reviewed verified by ORBi

Additional URL :

http://cdsads.u-strasbg.fr/abs/1997Sci...275.1909R

Available on ORBi :

since 18 February 2010

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We used the Danish Faint Object Spectrograph (DFOSC), a focal reducer-type instrument which allowed us to switch between spectra (3700 to 7000 Å; resolution: April and June: 15 Å, August and October: 18 Å), and imaging. The field-of-view was ≈13 arc min. The slit was aligned with the sun-comet axis.
Because no special filters centered on the cometary emissions were available to us, we chose filters from the standard ESO filters set [no. 514 at 3849 Å (band width 87 Å) for CN; no. 430 at 5117 Å (band width 56 Å) for C2]. Filter no. 510 at 4467 Å (band width 56 Å) has been used for continuum subtraction.
We used the medium-resolution spectrograph CARELEC in the range 3600 to 6800 Å (resolution: 7 Å). The slit length was 5 arc min. Spectra were taken with different slit orientations and averages obtained from these spectra.
Z. Sekanina and H. Boehnhardt, IAU Circular 6542 (1997); M. R. Kidger et al., in preparation.
Z. Sekanina and H. Boehnhardt, IAU Circular 6542 (1997); M. R. Kidger et al., in preparation.
Dramatic changes in dust distribution were observed recently [for example, see J. Lecacheux and F. Colas, IAU Circular 6560 (1997)].
M. F. A'Hearn et al., Astron. J. 89 579 (1984). Here, A is the albedo, f is the filling factor (ratio between total cross section of grains and area of the field of view), and ρ is the radius of the circular field of view.
The calculations are based on isotropic hydrodynamical modeling of the gas-dust interaction using CO and H2O molecules weighted by their respective mass production rates. This model accounts for the variation of thermal gas velocity with nucleus temperature as 280 K/√rh. To correct for the dependence of magnitude on phase angle, a factor of 0.03 mag/degree was used, as measured in comet Bowell at 3.7 to 5.6 AU. [R. L. Newburn and H. Spinrad, Astron. J. 90, 2591, (1985); J. F. Crifo, Astron. Astrophys. 187, 438, (1987); K. Meech and D. Jewitt, ibid., p. 585.
The calculations are based on isotropic hydrodynamical modeling of the gas-dust interaction using CO and H2O molecules weighted by their respective mass production rates. This model accounts for the variation of thermal gas velocity with nucleus temperature as 280 K/√rh. To correct for the dependence of magnitude on phase angle, a factor of 0.03 mag/degree was used, as measured in comet Bowell at 3.7 to 5.6 AU. [R. L. Newburn and H. Spinrad, Astron. J. 90, 2591, (1985); J. F. Crifo, Astron. Astrophys. 187, 438, (1987); K. Meech and D. Jewitt, ibid., p. 585.
The calculations are based on isotropic hydrodynamical modeling of the gas-dust interaction using CO and H2O molecules weighted by their respective mass production rates. This model accounts for the variation of thermal gas velocity with nucleus temperature as 280 K/√rh. To correct for the dependence of magnitude on phase angle, a factor of 0.03 mag/degree was used, as measured in comet Bowell at 3.7 to 5.6 AU. [R. L. Newburn and H. Spinrad, Astron. J. 90, 2591, (1985); J. F. Crifo, Astron. Astrophys. 187, 438, (1987); K. Meech and D. Jewitt, ibid., p. 585.
M. F. A'Hearn, R. L. Millis, D. G. Schleicher, D. J. Osip, P. V. Birch, Icarus 118, 223 (1995).
J. K. Davies et al., ibid., in press.
D. Jewitt, in Comets in the Post-Halley Era, R. L. Newburn, M. Neugebauer, J. Rahe, Eds. (Kluwer, Dordrecht, 1991) pp. 19-65.
All spectra were bias-subtracted, flatfielded, and extinction-corrected. The contribution from the night sky was determined from separate sky exposures. Variability in intensity of the [OI] emission at 5577 Å led to under-and oversubtraction in some cases. The underlying continuum of solar light reflected by the cometary dust was subtracted using a solar atlas [R. L. Kurucz et al., Sunspot, National Solar Observatory, (1984)] smoothed to the resolution of the cometary spectra, or using spectra of jovian satellites, when possible. Absolute calibration was performed using standard stars observed on the same night.
A. Fitzsimmons and I. M. Cartwright, Mon. Not. R. Astron. Soc. 278, L37 (1996).
_, IAU Circular 6361 (1996).
K. Jockers, T. Credner, N. Karpov, A. Sergeev, IAU Circular 6468 (1996).
N. Biver et al., Nature 380, 137 (1996); D. Jewitt, M. Senay, H. Matthews, Science 271, 1110 (1996).
N. Biver et al., Nature 380, 137 (1996); D. Jewitt, M. Senay, H. Matthews, Science 271, 1110 (1996).
H. A. Weaver et al., IAU Circular 6376 (1996).
M. F. A'Hearn et al., Icarus 64, 1, (1985).
A. Tegler and S. Wyckoff, Astrophys. J. 343, 445 (1989) and references therein.
B. L. Lutz, Astrophys. J. 315, L147 (1987).
C. Arpigny, in Molecules and Grains in Space, AIP Conf. Proc. 312, I. Nenner, Ed. (AIP Press, New York, 1994), pp. 205-239.
L. Haser, Bull. Acad. R. Belg., Classes Ser. 5, 43 (1957).
A. Cochran, E. S. Barker, T. F. Ramseyer, A. D. Storrs, Icarus 98, 151 (1992).
U. Fink and M. Hicks, Astrophys. J. 459, 729 (1996).
In particular for C2, for which the scale lengths and its scaling with rh differ significantly in the literature, this is an illustration of how difficult it is to constrain a unique set of parameters. Moreover, although the predicted profiles are similar, the resulting production rates can differ by 30% depending on the scale lengths used. We chose for all species the scale - lengths given by (22); g-factors for C3 from (8), for CN from: D. Schleicher, thesis, University of Maryland (1983); others from (22).
N. Biver et al., Science 275, 1915 (1997).
J. Crovisier et al., Astron. Astrophys. 315, L385 (1996).
T. Yamamoto, ibid. 142, 31, (1985).
M. Womack, D. Suswal, S. A. Stern, D. Slater, M. Festou, Bull. Am. Astron. Soc. 28, 1091 (1996).
M. F. A'Hearn et al., Nature 324, 649 (1986).
A. Dutrey et al., IAU Circular 6364 (1996); W. M. Irvine et al., Nature 383, 418 (1996).
A. Dutrey et al., IAU Circular 6364 (1996); W. M. Irvine et al., Nature 383, 418 (1996).
This paper is based on observations at the European Southern Observatory (ESO), Chile (prop. 57.F-0396), and the Observatoire de Haute Provence, France. We gratefully acknowledge the collaboration with members of the ESO ROSETTA/ISO target comets imaging team in the context of their observing programs at ESO [57.F-0274, 58.F-0431 (ESO time)], whose members are H. Boehnhardt, L. Colangeli, G. Cremonese, J. Crovisier, M. Fulle, L. Jorda, H. Rauer, H. Rickman, R. Schulz, G. Schwehm, and R. M. West. We thank also V. Buat and D. Burgarella, who gave us some of their observing time. H.R. acknowledges the support of an European Space Agency external research fellowship.