{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,26]],"date-time":"2026-09-26T23:16:20Z","timestamp":1790464580535,"version":"4.1.0"},"reference-count":39,"publisher":"American Association for the Advancement of Science (AAAS)","issue":"5308","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Science"],"published-print":{"date-parts":[[1997,3,28]]},"abstract":"<jats:p>\n            Analysis of Hubble Space Telescope (HST) images of comet Hale-Bopp (C\/1995 O1) suggests that the effective diameter of the nucleus is between 27 to 42 kilometers, which is at least three times larger than that of comet P\/Halley. The International Ultraviolet Explorer and HST spectra showed emissions from OH (a tracer of H\n            <jats:sub>2<\/jats:sub>\n            O) and CS (a tracer of CS\n            <jats:sub>2<\/jats:sub>\n            ) starting in April 1996, and from the CO Cameron system (which primarily traces CO\n            <jats:sub>2<\/jats:sub>\n            ) starting in June 1996. The variation of the H\n            <jats:sub>2<\/jats:sub>\n            O production rate with heliocentric distance was consistent with sublimation of an icy body near its subsolar point. The heliocentric variation in the production rates of CS\n            <jats:sub>2<\/jats:sub>\n            and dust was different from that of H\n            <jats:sub>2<\/jats:sub>\n            O, which implies that H\n            <jats:sub>2<\/jats:sub>\n            O sublimation did not control the CS\n            <jats:sub>2<\/jats:sub>\n            or dust production during these observations.\n          <\/jats:p>","DOI":"10.1126\/science.275.5308.1900","type":"journal-article","created":{"date-parts":[[2002,7,27]],"date-time":"2002-07-27T09:50:14Z","timestamp":1027763414000},"page":"1900-1904","source":"Crossref","is-referenced-by-count":91,"title":["The Activity and Size of the Nucleus of Comet Hale-Bopp (C\/1995 O1)"],"prefix":"10.1126","volume":"275","author":[{"given":"H. A.","family":"Weaver","sequence":"first","affiliation":[{"name":"H. A. Weaver, P. D. Feldman, J. B. McPhate, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"P. D.","family":"Feldman","sequence":"additional","affiliation":[{"name":"H. A. Weaver, P. D. Feldman, J. B. McPhate, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"M. F.","family":"A'Hearn","sequence":"additional","affiliation":[{"name":"M. F. A'Hearn and M. Haken, Department of Astronomy, University of Maryland, College Park, MD 20742, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"C.","family":"Arpigny","sequence":"additional","affiliation":[{"name":"C. Arpigny, Institut d'Astrophysique, Universit\u00e9 de Li\u00e8ge, B-4000 Li\u00e8ge, Belgium."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"J. C.","family":"Brandt","sequence":"additional","affiliation":[{"name":"J. C. Brandt, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"M. C.","family":"Festou","sequence":"additional","affiliation":[{"name":"M. C. Festou, Observatoire Midi-Pyr\u00e9n\u00e9es, 14 avenue E. Belin, F-31400, Toulouse, France."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"M.","family":"Haken","sequence":"additional","affiliation":[{"name":"M. F. A'Hearn and M. Haken, Department of Astronomy, University of Maryland, College Park, MD 20742, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"J. B.","family":"McPhate","sequence":"additional","affiliation":[{"name":"H. A. Weaver, P. D. Feldman, J. B. McPhate, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"S. A.","family":"Stern","sequence":"additional","affiliation":[{"name":"S. A. Stern, Southwest Research Institute, Space Science Department, Boulder Extension Office, 1050 Walnut Drive, Suite 426, Boulder, CO 80302, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"G. P.","family":"Tozzi","sequence":"additional","affiliation":[{"name":"G. P. Tozzi, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Florence, Italy."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"221","reference":[{"key":"e_1_3_1_2_2","author":"Hale A.","year":"1995","unstructured":"Hale A., Bopp T., IAU Circular 6187 (1995).","journal-title":"IAU Circular 6187"},{"key":"e_1_3_1_3_2","doi-asserted-by":"publisher","DOI":"10.1126\/science.271.5252.1110"},{"key":"e_1_3_1_4_2","doi-asserted-by":"crossref","first-page":"137","DOI":"10.1038\/380137a0","volume":"380","author":"Biver N.","year":"1996","unstructured":"Biver N., et al., Nature 380, 137 (1996).","journal-title":"Nature"},{"key":"e_1_3_1_5_2","unstructured":"The WFPC2 consists of three wide-field mode charged-coupled devices (CCDs) having 0.0996 arc sec pixel \u22121 and one planetary mode CCD having 0.0455 arc sec per pixel. The point spread function (PSF) of the planetary mode has a full-width at half-maximum of \u223c0.070 arc sec which projects to 250 km at a geocentric distance of 5 AU. Further information on the WFPC2 is available at http:\/\/www.stsci.edu\/ftp\/instrument_news\/WFPC2\/wfpc2_top.html."},{"key":"e_1_3_1_6_2","unstructured":"The FOS is a versatile instrument that can provide moderate and low resolution spectra over the wavelength range from 1140 \u00c5 to 9000 \u00c5 by employing multiple gratings and two one-dimensional digicon detectors coated with different photocathodes. During our observations we used the G190H and G270H gratings which together covered the wavelength range from 1570 \u00c5 to 3300 \u00c5 at a resolving power of \u223c1000 for the cometary emissions having a sharply-peaked spatial distribution. Further information on the FOS is available http:\/\/www.stsci.edu\/ftp\/instrument_news\/FOS\/topfos.html."},{"key":"e_1_3_1_7_2","unstructured":"Weaver H. A. et al. Science vol. 263 (1994) p. 787The WFPC2 CCD signal measured through the F675W filter and attributed to the nucleus can be converted to an R magnitude in the Landolt-Kron-Cousins photometric system using standard relations given in (4). Then the diameter of the nucleus d N (km) can be calculated using:\n\nwhere m sun (= \u221227.10) is the R magnitude of the sun m comet is the R magnitude of the nucleus and A p is the geometric albedo."},{"key":"e_1_3_1_8_2","first-page":"L43","volume":"293","author":"Lamy P. L.","year":"1995","unstructured":"Lamy P. L., Toth I., Astron. Astrophys. 293, L43 (1995).","journal-title":"Astron. Astrophys."},{"key":"e_1_3_1_9_2","unstructured":"Lamy P. L. Toth I. Weaver H. A. Astron. Astrophys. in preparation."},{"key":"e_1_3_1_10_2","unstructured":"Wallace L. V. Miller F. D. Astron. J. vol. 63 (1958) p. 213The results from this report can be used to demonstrate that the coma flux observed in a circular aperture of fixed angular dimensions scales as \u0394 \u22121 . The flux from the nucleus is independent of aperture size and scales as \u0394 \u22122 ."},{"key":"e_1_3_1_11_2","volume-title":"Comets in the Post-Halley Era","author":"Jewitt D. C.","year":"1991","unstructured":"Jewitt D. C., Comets in the Post-Halley Era, , Newburn R. L., Neugebauer M., Rahe J., Eds. (Kluwer, Dordrecht, 1991)."},{"key":"e_1_3_1_12_2","unstructured":"All of our non-trailed HST images taken in planetary mode show a brightness cusp at the peak pixel that we interpret as the signature of the nucleus. However if icy grains dominated the dust population within a few hundred kilometers of the nucleus and evaporated into lower albedo particles outside this region then the brightness cusp could be due to coma rather than the nucleus. On the other hand a continuous degradation of dust albedo with cometocentric distance would steepen the coma surface brightness profile causing us to underestimate the size of the nucleus. Similarly dust fragmentation in the coma could cause us to underestimate or overestimate the size of the nucleus depending on the exact nature of the fragmentation."},{"key":"e_1_3_1_13_2","first-page":"807","volume":"187","author":"Keller H. U.","year":"1987","unstructured":"Keller H. U., et al., Astron. Astrophys. 187, 807 (1987).","journal-title":"Astron. Astrophys."},{"key":"e_1_3_1_14_2","unstructured":"While the signal-to-noise ratio in the peak pixel is large (over 100) the error in estimating the size of the nucleus is determined by systematic effects. In particular the derived size depends on the extrapolation of the coma into the unresolved region. Light scattered from a 42-km nucleus only contributes \u223c37% of the brightness in the peak pixel so the coma dominates the observed light distribution even in the core of the image. The nucleus has to be large in order to detect its signature in the presence of such a bright coma and a Halley-sized object would be undetectable with HST."},{"key":"e_1_3_1_15_2","doi-asserted-by":"crossref","first-page":"223","DOI":"10.1006\/icar.1995.1190","volume":"118","author":"A'Hearn M. F.","year":"1995","unstructured":"A'Hearn M. F., et al., Icarus 118, 223 (1995).","journal-title":"Icarus"},{"key":"e_1_3_1_16_2","unstructured":"Kidger M. R. et al. Astrophys. J. Lett. in preparation."},{"key":"e_1_3_1_17_2","author":"Weaver H. A.","year":"1996","unstructured":"Weaver H. A., IAU Circular 6376 (1996).","journal-title":"IAU Circular 6376"},{"key":"e_1_3_1_18_2","doi-asserted-by":"crossref","first-page":"449","DOI":"10.1016\/0019-1035(81)90193-7","volume":"47","author":"Weaver H. A.","year":"1981","unstructured":"Weaver H. A., Feldman P. D., Festou M. C., A'Hearn M. F., Keller H. U., Icarus 47, 449 (1981).","journal-title":"Icarus"},{"key":"e_1_3_1_19_2","doi-asserted-by":"crossref","unstructured":"Schleicher D. G. A'Hearn M. F. Astrophys. J. 331 1058 (1988);","DOI":"10.1086\/166622"},{"key":"e_1_3_1_19_3","doi-asserted-by":"crossref","first-page":"524","DOI":"10.1086\/166674","volume":"332","author":"Schloerb F. P.","year":"1988","unstructured":"Schloerb F. P., Astrophys. J. 332, 524 (1988).","journal-title":"Astrophys. J."},{"key":"e_1_3_1_20_2","unstructured":"Festou M. C. Astron. Astrophys. 96 69 (1981);"},{"key":"e_1_3_1_20_3","doi-asserted-by":"crossref","first-page":"164","DOI":"10.1006\/icar.1994.1014","volume":"107","author":"Budzien S. A.","year":"1994","unstructured":"Budzien S. A. , Festou M. C. , Feldman P. D., Icarus 107, 164 (1994).","journal-title":"Icarus"},{"key":"e_1_3_1_21_2","first-page":"385","volume":"107","author":"Jackson W. M.","year":"1982","unstructured":"Jackson W. M., Halpern J. B., Feldman P. D., Rahe J., Astron. Astrophys. 107, 385 (1982).","journal-title":"Astron. Astrophys."},{"key":"e_1_3_1_22_2","unstructured":"Haser L. Bull. Acad. R. Sci. Li\u00e8ge vol. 43 (1957) p. 740The CS 2 lifetime (500 r h 2 s) is so short that we assume that collisions equilibrate the CS 2 and CS velocities to the same value (0.8 r h \u22120.5 km s \u22121 and 0.85 r h \u22120.5 km s \u22121 for the HST and IUE data respectively). Examination of the relevant collision rates indicates that this assumption is justified for most of the 1996 observations but may not be valid at the larger values of r h . Using a vectorial model raises Q CS 2 by a factor of \u223c2 relative to the Haser model result at all values of r h . Thus using a single model either Haser or vectorial does not change the power law index for the r h variation of Q CS 2 . Using a vectorial model at large r h and a Haser model at small r h would produce a smaller power law index which strengthens our conclusion that Q CS 2 and Q H 2 O had different variations with r h . We assumed that a CS molecule is produced for every CS 2 molecule that is destroyed and we used a CS lifetime of 1 \u00d7 10 5 r h 2 s."},{"key":"e_1_3_1_23_2","doi-asserted-by":"crossref","first-page":"155","DOI":"10.1007\/BF00897085","volume":"21","author":"Cowan J. J.","year":"1979","unstructured":"Cowan J. J., A'Hearn M. F., Moon and Planets 21, 155 (1979).","journal-title":"Moon and Planets"},{"key":"e_1_3_1_24_2","unstructured":"At large r h the activity in Hale-Bopp was apparently driven by the sublimation of CO ice (2 3) which means that dust grains in the coma may have retained a H 2 O ice mantle. Owing to their low efficiency at radiating heat micrometer-sized grains can become warmer than the nucleus which means that H 2 O in the coma at large r h could be due primarily to sublimation from these icy grains and that our values of Q H 2 O no longer refer to H 2 O production from the nucleus. As is typically the case for comets H 2 O sublimation from the nucleus of Hale-Bopp presumably became the dominant source of H 2 O in the coma at some point. Perhaps the best evidence for the latter is the agreement between our model sublimation curves and the observed values of Q H 2 O . The activation of several new vents on the surface of the nucleus during mid-1996 as observed in ground-based images of Hale-Bopp may also have signaled the transition from a CO-dominated comet to a H 2 O-dominated one."},{"key":"e_1_3_1_25_2","unstructured":"Crovisier J. et al. paper on the radio observations of Hale-Bopp presented at the 28th Annual Meeting of the Division of Planetary Sciences of the American Astronomical Society; Tucson AZ.  (22 to 26 October 1996)."},{"key":"e_1_3_1_26_2","doi-asserted-by":"crossref","first-page":"374","DOI":"10.1086\/173732","volume":"422","author":"Weaver H. A.","year":"1994","unstructured":"Weaver H. A., et al., Astrophys. J. 422, 374 (1994).","journal-title":"Astrophys. J."},{"key":"e_1_3_1_27_2","unstructured":"Assuming that CO 2 is flowing outward from the nucleus the production rate is given by: Q CO 2 = (7.25 \u00d7 10 18 ) v \u03b8 r h 2 \u0394 B \/ g where g is the rate constant v = 0.8 r h \u22120.5 km s \u22121 B is the observed brightness of the Cameron (1 0) band in rayleighs and \u03b8 is the diameter of the equivalent circular aperture of 2.4 arc sec."},{"key":"e_1_3_1_28_2","unstructured":"Crovisier J. et al. Science vol. 275 (1997) p. 1904We recomputed Q CO 2 derived from the ISO observations using an outflow velocity of 0.8 r h \u22120.5 in order to be consistent with the assumptions made in analyzing the HST data."},{"key":"e_1_3_1_29_2","unstructured":"A'Hearn M. F. Schleicher D. G. Feldman P. D. Millis R. L. Thompson D. T. Astron. J. vol. 89 (1984) p. 579From the HST images we calculated Af \u03c1 using a synthetic aperture having a diameter of 2 arc sec which is close to the effective diameter of our most commonly used FOS aperture (2.4 arc sec). We found that Af \u03c1 varied with aperture size typically at the 10 to 30% level probably due to temporal variability in the comet. By comparing the HST imaging and spectral data we found empirically that Af \u03c1 near 7000 \u00c5 the effective wavelength of the F675W filter used for the WFPC2 observations was \u223c1.9 times larger than Af \u03c1 near 2950 \u00c5. Thus we multiplied the raw IUE Af \u03c1 values near 2950 \u00c5 by 1.9 to convert them to their equivalent \u201coptical\u201d values. The Af \u03c1 values were converted to a common phase angle (the sun-comet-Earth angle) \u03d5 of 0\u00b0 by multiplying the raw values by 10 (0.4)(0.035)\u03d5 . A different choice for the phase law is unlikely to affect our conclusions as Hale-Bopp was observed over a narrow range in phase angle."},{"key":"e_1_3_1_30_2","unstructured":"For dust having an average radius a (in micrometers) density d (in grams per cubic centimeter) geometric albedo A p and flowing outward from the nucleus with velocity v dust (in kilometers per second) the dust mass production rate Q dust (in kilograms per second) is given by: Q dust = (0.67) adv dust Af \u03c1\/ A p where Af \u03c1 is in meters. We calculated Q dust using v dust = 0.13 r h \u22120.5 (30) a = 10 d = 1 and A p = 0.04 (Table 1 and Fig. 4)."},{"key":"e_1_3_1_31_2","unstructured":"Sekanina Z. Astron. Astrophys. vol. 314 (1996) p. 957From a detailed analysis of the dust coma this author derived a dust ouflow velocity ( v dust ) of \u223c0.05 km s \u22121 at r h = 6.82 AU and we have additionally assumed that v dust = 0.05 ( r h \/6.82) \u22120.5 ."},{"key":"e_1_3_1_32_2","volume-title":"Atlas of Cometary Spectra","author":"Arpigny C.","year":"1997","unstructured":"Arpigny C., et al., Atlas of Cometary Spectra (Kluwer, Dordrecht, 1997)."},{"key":"e_1_3_1_33_2","doi-asserted-by":"crossref","unstructured":"Kam\u00e9l L. Icarus vol. 122 (1996) p. 428and (14).","DOI":"10.1006\/icar.1996.0134"},{"key":"e_1_3_1_34_2","unstructured":"A spectrum ending at 14:05 universal time (UT) on 23 September 1996 had essentially the same continuum flux as other spectra that were taken between 10:30 and 14:05 UT. (The spectra were not continuously recorded during this latter period because the HST periodically passes behind the Earth at which times the comet was not visible from HST. The HST orbital period is 96 min and observations are generally limited to a duration of \u223c30 min each orbit.) Following a gap in our coverage due to Earth occultation a 2-min spectrum starting at 13:41 UT had a continuum level that was 3.4 times larger than that recorded during the earlier times. In addition three subsequent 2-min spectra showed the continuum intensity monotonically increasing at the rate of \u223c1.2% min \u22121 ."},{"key":"e_1_3_1_35_2","unstructured":"We ruled out pointing error as the source of the observed temporal variation by verifying that the flux measured in spectra taken immediately before the outburst was essentially identical to that measured during observations spanning up to \u223c6.5 hours earlier. A solar-type star entering the aperture and having a visual magnitude of \u223c11.5 could have produced the observed increase in the continuum but no such object was present in the cometary field. Furthermore another object entering the aperture would not explain the observed increase in CS emission. During the outburst the spatial distribution of the continuum became markedly more peaked towards the nucleus which is consistent with a dust outburst originating at the nucleus of the comet."},{"key":"e_1_3_1_36_2","unstructured":"For spherically symmetric outflow of dust from the nucleus with velocity v it is easy to show that the total number of grains n q in a circular aperture of radius \u03c1 is given by n q = (\u03c0\/2) Q q \u03c1\/ v where Q q is the dust production rate (in particles per second) under steady-state conditions. The number of extra dust grains n o created during an outburst of duration t is given by n o = Q o t where Q o is the extra production rate above the quiescent value averaged over the duration of the outburst. Since n o \/ n q = 2.4 \u03c1 = 2570 km and t = 4635 s for our observations the ratio of these two production rates is given by 2.1\/ v when v is in kilometers per second. Using our adopted value for v (0.076 km s \u22121 ) yields a Q ratio of 28. In cometary work it is usually assumed that the dust velocity is given by v \u223c 0.5 r h \u22120.5 [N. T. Bobrovnikov Astron. J. 59 357 (1954)] which gives a Q ratio of 7 and implies that the total dust production rate averaged over the outburst was eight times the quiescent value."},{"key":"e_1_3_1_37_2","unstructured":"Assuming that all of the molecules produced during the outburst are contained in the observing aperture the number of daughter molecules n d at time t following the outburst is related to the number of parent molecules n p produced during the outburst by n d = n p (1 \u2212 e \u2212 t \/\u03c4 ) where \u03c4 is the parent lifetime. Using our adopted lifetimes for CS 2 and H 2 O and an outburst duration of 4635 s we see that the increase in the number of CS molecules should be \u223c64% of the increase in the number of CS 2 molecules while the number of extra OH molecules should increase by less than 1% of the increase in H 2 O molecules."},{"key":"e_1_3_1_38_2","unstructured":"Support for this work was provided by NASA through grant numbers GO-05844 and GO-06663 from the Space Telescope Science Institute (STScI) which is operated by the Association of Universities for Research in Astronomy Inc. under NASA contract NAS5-26555. C. Arpigny gratefully acknowledges financial support by the Belgian Fonds National de la Recherche Scientifique. We thank A. Lubenow and A. Storrs of the STScI for expertly planning the HST observations of Hale-Bopp. We also express our gratitude to W. Wamsteker and H. Andernach for their strong support of the IUE Hale-Bopp program."}],"container-title":["Science"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.science.org\/doi\/pdf\/10.1126\/science.275.5308.1900","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2024,1,13]],"date-time":"2024-01-13T03:06:46Z","timestamp":1705115206000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.science.org\/doi\/10.1126\/science.275.5308.1900"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1997,3,28]]},"references-count":39,"journal-issue":{"issue":"5308","published-print":{"date-parts":[[1997,3,28]]}},"alternative-id":["10.1126\/science.275.5308.1900"],"URL":"https:\/\/doi.org\/10.1126\/science.275.5308.1900","relation":{},"ISSN":["0036-8075","1095-9203"],"issn-type":[{"value":"0036-8075","type":"print"},{"value":"1095-9203","type":"electronic"}],"subject":[],"published":{"date-parts":[[1997,3,28]]}}}