O1 Hale-Bopp Research Articles

A determination of the HDO/H2O ratio in comet C/1995 O1 (Hale-Bopp).

Deuterated water (HDO) was detected in comet C/1995 O1 (Hale-Bopp) with the use of the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. The inferred D/H ratio in Hale-Bopp's water is (3.3 +/- 0.8) x 10(-4). This result is consistent with in situ measurements of comet P/Halley and the value found in C/1996 B2 (Hyakutake). This D/H ratio, higher than that in terrestrial water and more than 10 times the value for protosolar H2, implies that comets cannot be the only source for the oceans on Earth.

Evidence for Dust-related X-Ray Emission from Comet C/1995 O1 (Hale-Bopp)

We report the discovery of X-ray emission from comet C/1995 O1 (Hale-Bopp) by the LECS instrument on board BeppoSAX on 1996 September 10-11. The 0.1-2.0 keV luminosity decayed by a factor of 2 on a timescale of ~10 hr with a mean value of 5×1016 ergs s−1. The spectrum is well fitted by a thermal bremsstrahlung model with a temperature of 0.29±0.06 keV or a power law with a photon index of 3.1+ 0.6−0.2. The lack of detected C and O line emission places severe constraints on many models for cometary X-ray emission, especially those that involve X-ray production in cometary gas. The luminosity is a factor of at least 3.4 greater than measured by the Extreme Ultraviolet Explorer (EUVE) 4 days later. This difference may be related to the emergence from the nucleus on 1996 September 9 of a dust-rich cloud. Over the next few days, the cloud continued to expand, becoming increasingly tenuous until it had reached an extent of ~3×105 km (or ~2') by the start of the EUVE observation. We speculate that the observed reduction in X-ray intensity is evidence for dust fragmentation. These results support the view that cometary X-ray emission arises from the interaction between solar X-rays and cometary dust.

QUANTITATIVE MORPHOLOGY OF C/1995 O1 (HALE-BOPP) IN FEBRUARY - APRIL 1997

Extensive widefield CCD direct imaging of C/1995 O1 (Hale-Bopp) at UBVRI was carried out at Hoher List Observatory with the 1.06 m telescope (field of view 20′ × 20′) and at Potsdam Observatory with the 0.70 m telescope (field of view 8′ × 8′). The corresponding spatial resolution is 850–1000 km pix-1and 525–590 km pix-1, respectively. The data covers 25 nights from February 20 to April 21, 1997.

The Infrared Spectral Energy Distribution And Polarization Of Comet C/1995 O1 (Hale–Bopp) During 1997

Comets, such as C/1995 O1 (Hale-Bopp), are important to studies of the origins of the solar system because they are believed to be frozen reservoirs of the most primitive pre-solar dust grains and ices. Here, we report 1.2–18.5 μm infrared (IR) spectrophotometric and polarimetric observations of comet Hale-Bopp. Our measurements of the spectral energy distribution (SED) and IR polarization near perhelion passage suggest that emission from the coma was dominated by scattering and thermal emission from sub-micron sized dust grains. Hale-Bopp's surprising brightness may have been largely a result of the properties of its coma grains rather than the size of its nucleus. The thermal emission continuum from the grains had a superheat of S = Tcolor/TBB ≥ 1.7, the peak of the 10 μm silicate emission feature was 1.7 mags above the carbon grain continuum, and the albedo (reflectivity) of the grains was ≥ 0.4 at a scattering angles, θ ≥ 135°

Neutral Sodium from Comet Hale-Bopp: A Third Type of Tail

We report on the discovery and analysis of a striking neutral sodium gas tail associated with comet C/1995 O1 Hale-Bopp. Sodium D line emission has been observed at heliocentric distance r≤1.4 AU in some long-period comets, and the presence of neutral sodium in the tailward direction of a few bright comets has been noted, but the extent, and in particular the source, has never been clear. Here we describe the first observations and analysis of a neutral sodium gas tail in comet Hale-Bopp, which is entirely different from the previously known ion and dust tails. We show that the observed characteristics of this third type of tail are consistent with it being produced by radiation pressure due to resonance fluorescence of sodium atoms and that the lifetime for photoionization is consistent with recent theoretical calculations.

The Heliocentric Evolution of Key Species in the Distantly-Active Comet C/1995 O1 (Hale-Bopp)

view Abstract Citations (25) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Heliocentric Evolution of Key Species in the Distantly-Active Comet C/1995 O1 (Hale-Bopp) Womack, Maria ; Festou, M. C. ; Stern, S. Alan Abstract Comet Hale-Bopp (C/1995 01) presents the first opportunity to study physical and chemical changes in the coma of a bright, active comet at large heliocentric distances with modern millimeter-wavelength spectrometers. We obtained mm-wave spectra of CH3OH, CO, and H2CO in Hale-Bopp on 29 dates when it was beyond 4 AU. We report the first detection of CH3OH in Hale-Bopp at 5.0 AU. Additionally, we found that CO production went through three distinct phases: (i) an initial, rapid increase, (ii) quasi-saturation, and then (iii) a renewed, but less rapid increase. The abrupt renewal of the CO production rate increase took place near both the onset of H2O sublimation and the first detections of CH3OH and HCN, suggesting a causal relationship. Line shape and velocity offset information in our spectra give important clues to the production mechanisms of the three species. Linewidths were relatively narrow (0.3 km s-1) for CO and much wider (1-2 km s-1) for CH3OH and H2CO. Line profiles of CO were substantially blueshifted with respect to the comet's frame of reference by an average of 0.3 km s-1, while CH3OH and H2CO emission appeared essentially at rest with respect to the comet's frame. Based on these findings, we infer that the CO we observed was produced primarily at the nucleus in jets, rather than from an extended source, and that the majority of both the CH3OH and H2CO appear instead to be released as daughter products from the dissociation of heavier molecules. Publication: The Astronomical Journal Pub Date: December 1997 DOI: 10.1086/118687 Bibcode: 1997AJ....114.2789W Keywords: COMETS: INDIVIDUAL: HALE BOPP full text sources ADS |

Pre-perihelion CCD photometry of Comet 1995 01 (Hale-Bopp)

Systematic CCD photometry of Comet 1995 O1 (Hale-Bopp) began in early August 1995 shortly after its discovery ( IAU Circular 6187) and continued until mid-November 1996. The light curve derived from a 34″ square centered on the nucleus shows clearly and objectively how the inner regions of the comet brightened during this 15 month period. Possible connections between sudden brightenings and reported outbursts are investigated. During the interval August–December 1995, the magnitude of the comet showed strong evidence of a periodicity of 20±5 days with a full amplitude of approximately 0.20 mag. It is noteworthy that this result spans both the period of 18 days suggested by Sekanina (1995, 1996) and the “superperiod” of 22±2 days reported by Jorda et al. (1997). However, in 1996 neither this periodicity nor any other could be detected with certainty in the photometric data.

Measurement of Submicron Grains in the Coma of Comet Hale-Bopp C/1995 O1 during 1997 February 15–20 UT

We present 1.20-18.5 μm infrared (IR) spectrophotometric measurements of comet C/1995 O1 (Hale-Bopp) during 1997 February 15 and 20 UT. The spectral energy distribution (SED) was dominated by scattering and thermal emission from submicron sized dust grains that were unusually small. Hale-Bopp's surprising brightness may have been largely a result of the properties of its coma grains rather than the size of its nucleus. The thermal emission continuum from the grains had a superheat of S=Tcolor/TBB ≈ 1.84, the peak of the 10 μm silicate emission feature was 1.81 mag above the carbon grain continuum, and the albedo (reflectivity) of the grains was ≈ 0.41 at a scattering angle of θ ≈ 144°. These are the highest values for these empirical parameters ever observed in 20 years of optical/IR measurements of bright comets. The observations indicate that the optically important grains dominating the visual scattering and near-IR emission from the coma had an average radius of a≤0.4 μm. The strong silicate feature is produced by grains with a similar size range. These dust radii are comparable to the radii of the grains that condense in the outflows of some novae ("stardust") but still about 10 times larger than the average radius of the grains that produce the general interstellar extinction.

Evidences for extended sources and temporal modulations in molecular observations of C/1995 O1 (Hale-Bopp) at the IRAM interferometer

Comet C/1995 O1 (Hale-Bopp) has been observed on October 5 and 25, 1996 and from March 6 to March 22, 1997 with the Institut de Radioastronomie Millimetrique (IRAM) interferometer at Plateau de Bure (France). Millimetre lines of HCN,HNC, CO, H2CO, CH3OH, H2S, CS and SO were mapped with spatial resolutions of 1.5–3.5 arc sec. These observations allow us to investigate whether these species are released by the nucleus or produced in the coma by extended sources or photo-processes. The brightness distribution of the HCN J (1-0) line is consistent with release from the nucleus. The HNC J (1-0) distribution deviates from that of HCN in the innermost coma, and indicates production of HNC in the coma. This is in agreement with the heliocentric variation of the HNC/HCN ratio (Biver et al., 1997, Science 275, 1915; Irvine et al., 1998, this issue) and formation by chemical reactions (Rodgers and Charnley, 1998, Ap. J. 501, L227; Irvine et al., 1998, Nature 393, 547). There is clear evidence that SO is a photo dissociation product. The observations also confirm that H2CO is mainly produced by an extended source, as first evidenced in comet P/Halley. The contribution of the nucleus to the total H2CO production rate does not exceed 6%. The molecular lines have also been monitored hourly with the five antennas of the interferometer in single-dish mode. The line velocity shifts show aperiodic modulation linked to the nucleus rotation. The amplitude of the modulation differs from one species to another. The periodic modulation seen for the CO J (2-1) line on March 11 suggests that a significant fraction of CO is released continuously night and day by an active source situated at equatorial latitudes on the nucleus surface.

The interaction of C/1995 O1 Hale-Bopp with the solar wind as recorded in CoCam images: A progress report

The Isaac Newton Group’s CoCam instrument obtained wide-field (10°X 20°) CCD images of the H2O+ tail of Hale-Bopp on March 12–15, 19, 20, 25, 28, 29, 31, April1, 7, 9–13, 21, 23–29 and May 4, 1997. A 6185a filter recorded the distribution of H2O+; 6250a-centered continuum images were also obtained. Initial analysis has revealed the CoCam dataset to be an invaluable record of the large-scale structure of the comet's ion tail. Several images show evidence of upstream parabolic envelopes of ions reminiscent of those reported in C/1908 R1 Morehouse (Eddington A. S., Mon. Not. Roy. Astron. Soc. 70, 442–458, 1910). Studies of these features may help towards a better understanding of the tail ray phenomenon. During most of March and early April, the tail had a largely consistent quiescent appearance, with numerous rays exhibited, but no major disturbances; most probably as a result of being in the stream of fast polar solar wind. A significant kink propagated down the tail around April 9/10. Towards the end of April, as the comet entered more variable solar wind at near-equatorial heliographic latitudes, the tail's morphology became significantly more structured. Striking tail disturbances were recorded in late April and early May, when the comet was in the vicinity of the heliospheric current sheet. Analysis of the dataset continues.

Cometary volatiles

Comets are believed to be the most pristine material surviving from the origin of the Solar System. The nature of their volatiles should in principle provide chemical and physical clues to their formation environment in the solar nebula. Another important aspect of the study of comets is the extent to which they may incorporate relatively unprocessed interstellar material.Our knowledge of the composition of cometary ices has been greatly improved in this last decade. The years 1995-1996 were rich in new results, with the close approach to Earth of comet C/1996 B2 Hyakutake and the discovery of the bright comet C/1995 O1 Hale-Bopp at large heliocentric distance. We will present the current knowledge of the nature and abundances of cometary volatiles and mention some of the outstanding issues related to the origin of comets and their links to interstellar material.

HCO+ in the coma of comet Hale-Bopp.

Maps of comet C/1995 O1 (Hale-Bopp) in the millimeter-wave emission of the ion HCO+ revealed a local minimum near the nucleus position, with a maximum about 100,000 km in the antisolar direction. These observed features of the HCO+ emission require a low abundance of HCO+ due to enhanced destruction in the inner coma of the comet, within a region of low electron temperature (Te). To set constraints on the formation of HCO+ in the coma, as well as the location and magnitude of the transition to higher Te, the data are compared with the results of ion-molecule chemistry models.

Aperture Polarimetry And Photometry Of Comet Hale-Bopp

We present results of polarimetric and photometric observations of bright comet C/1995 O1 (Hale-Bopp) obtained at the 0.7 m telescope of Kharkov University Observatory from June 18, 1996 to April 24, 1997. The IHW and HB comet filters were used. The C2 and C3 production rates for Hale-Bopp are more than one order of magnitude larger and the dust production rates are more than two orders of magnitude larger than the Halley ones at comparable distances. Hence, Hale-Bopp was one of the most dusty comets. The average UC-BC and BC-RC colours of the dust were −0.02 and 0.13 mag, respectively. The polarization of comet Hale-Bopp at small phase angles of 4.8–13.0° was in good agreement with the date for comet P1/Halley at the same phase angles in spite of the fact that the heliocentric distances of comments differed nearly twice. However, at intermediate phase angles of 34–49° the polarization of comet Hale-Bopp was significantly larger than the polarization of the other dusty comets. It is the first case of such a large difference found in the continuum polarization of comets. The wavelength dependence of polarization for Hale-Bopp was steeper than for other dusty comets. The observed degree of polarization for the anti-sunward side of the coma was permanently higher than that for the sunward shell side. The polarization phase dependence of Hale-Bopp is discussed and compared with the polarization curves for other dusty comets. The peculiar polarimetric properties of comet Hale-Bopp are most likely caused by an over-abundance of small or/and absorbing dust particles in the coma.

INFRARED OBSERVATIONS OF DUST EMISSION FROM COMET HALE-BOPP

We present infrared imaging and photometry of the bright, giant comet C/1995 O1 (Hale-Bopp). The comet was observed in an extended infrared and optical observing campaign in 1996–1997. The infrared morphology of the comet was observed to change from the 6 to 8 jet “porcupine” structure in 1996 to the “pinwheel” structure seen in 1997; this has implications for the position of the rotational angular momentum vector. Long term light curves taken at 11.3 μm indicate a dust production rate that varies with heliocentric distance as ∶ r−1.4. Short term light curves taken at perihelion indicate a rotational periodicity of 11.3 hours and a projected dust outflow speed of ∶ 0.4 km s−1. The spectral energy distribution of the dust on October 31, 1996 is well modeled by a mixture of 70% silicaceous and 30% carbonaceous non-porous grains, with a small particle dominated size distribution like that seen for comet P/Halley (McDonnell et al., 1991), an overall dust production rate of 2 × 105 kg s−1, a dust-to-gas ratio of ∶5, and an albedo of 39%.

Mid-Infrared Spectro-Imaging Observations Of Comet Hale-Bopp

Comet C/1995 O1 (Hale-Bopp) was observed with camiras, the Saclay mid-infrared camera, mounted on the Nordic Optical Telescope (Roque de los Muchachos, La Palma), from April 14th to April 25th, 1997. This observing run was part of the European campaign devoted to Hale-Bopp observations from the Canary Islands (PI R. West). camiras spectro-imaging capabilities, achieved with a Circular Variable Filter (of spectral resolution R ≈ 50), were used to obtain spectra of the comet in the N atmospheric window (8–13 μm) over a large field of view (52″ × 78″), at a spatial resolution of ∼1 arcsec. Data were also collected at shorter wavelengths (in the L and M bands). The silicate dust feature around 10 μm is clearly apparent in the data. The shape of the feature varies continuously according to the position in the field. A dust model developed at Saclay in the framework of β-Pictoris dust disk studies was used to interpret the observations. The presence of both olivine and pyroxene with a high degree of crystallinity is needed to account for the observations. A change in the size distribution of the grains allows to reproduce the spatial change of the silicate feature according to the position in the field.

Long-term Evolution of the Outgassing of Comet Hale-Bopp From Radio Observations

C/1995 O1 (Hale-Bopp) has been observed on a regular basis since August 1995 at millimetre and submillimetre wavelengths using IRAM, JCMT, CSO and SEST radio telescopes. The production rates of eight molecular species (CO, HCN, CH3OH, H2CO,H2S, CS, CH3CN,HNC) have been monitored as a function of heliocentric distance(rh from 7 AU pre-perihelion to 4 AU post-perihelion. As comet Hale-Bopp approached and receded from the Sun, these species displayed different behaviours. Far from the Sun, the most volatile species were found in general relatively more abundant in the coma. In comparison to other species, HNC, H2CO and CS showed a much steeper increase of the production rate with decreasing rh. Less than 1.5 AU from the Sun, the relative abundances were fairly stable and approached those found in other comets near 1 AU. The kinetic temperature of the coma, estimated from the relative intensities of the CH3OH and CO lines, increased with decreasing rh, from about10 K at 7 AU to 110 K around perihelion. The expansion velocity of the gaseous species, derived from the line shapes, also increased with a law close torh 3.

Infrared Spectroscopy of Comet Hale-Bopp

High resolution (λ/δλ ∼ 20,000) spectra of comet C/1995 O1 (Hale-Bopp) in the 2–5 μm region were obtained during UT 2–5 March 1997 using CSHELL at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The heliocentric and geocentric distances of the comet were ∼1.1 AU and ∼1.5 AU,respectively. We detected emission lines of the gas-phase molecules H2O, 4, C2H6, C2H2, HCN, and CO and derived absolute production rates and relative abundances for all species. We also used the 2-dimensional nature of the CSHELL data to investigate the spatial distribution of the molecules and find evidence that CO was derived at least partly from an extended source in the coma.

The infrared spectrum of comet Hale-Bopp as seen by the Infrared Space Observatory

Spectra of comet C/1995 O1 (Hale-Bopp) were obtained with the Infrared Space Observatory (ISO) at medium resolution with the grating spectrometer in the photometer (PHT-S) and/or at high resolution with the short wavelength spectrometer (SWS) and long wavelength spectrometer (LWS) in April 1996 (Crovisier et al., 1996), September–October 1996 (Crovisier et al., 1997a, b) and December 1997, at distances from the Sun of 4.6, 2.9 and 3.9 AU, respectively. For the first time, high-resolution spectra of a comet covering the entire 2.4 to 200 μm spectral range were obtained.

The Spin Axis Position of C/1995 O1 (Hale-Bopp)

Monitoring of the near-nucleus activity of C/1995 O1 (Hale-Bopp) began in Teide Observatory in August 1995. During 1996 the comet was observed on 72 nights between March 26 and November 13. A permanent fan structure was observed towards the north during the whole period of observation. The position angle of the axis of this fan was measured and its variations with time were used to determine the position of the North Pole of the cometary nucleus.

Discovery of Mg-rich pyroxenes in comet C/1995 O1 (Hale-Bopp): Pristine grains revealed at perihelion

The NASA Ames HIFOGS spectrometer observed comet C/1995 O1 (Hale-Bopp) at epochs including 96 Oct 7–14 UT (2.8 AU), 97 Feb 14–15 UT (1.2 AU), 97 Apr 11 UT (0.93 AU), and 97 Jun 22, 25 UT (1.7 AU). The HIFOGS 7.5–13.5 μm spectrophotometry (R = 360 - 180) of the silicate feature at 2.8 AU is identical in shape to the ISO SWS spectra of comet Hale-Bopp (Crovisier et al., 1997); the strong 11.2 μm peak in the structured silicate feature is identified as olivine. Upon close passage to the sun, the HIFOGS spectra at 1.2 AU and 0.93 AU reveals strong peaks at 9.3 μm and 10.0 μm. The post-perihelion 10 μm silicate feature at 1.7 AU is weaker but has nearly the same shape as the pre-perihelion spectra at 1.2 AU, reverting to its pre-perihelion shape: there is no change in the dust chemistry by close passage to the sun. The appearance of the strong peaks at 9.3 μm and 10.0 μm at rh ≲ 1.7 AU is attributed to the rise in the contribution of pryoxenes (clino-pyroxene and orthopyroxene crystals) to the shape of the feature, and leads to the hypothesis that the pyroxenes are significantly cooler than the olivines. The pyroxenes are radiating on the Wien side of the blackbody at 2.8 AU and transition to the Rayleigh-Jeans tail of the blackbody upon closer approach to the Sun. Composite fits to the observed 10 μm silicate features using IDPs and laboratory minerals shows that a good empirical fit to the spectra is obtained when the pryoxenes are about 150 K cooler than the olivines. The pyroxenes, because they are cooler and contribute signficantly at perihelion, are more abundant than the olivines. The perihelion temperature of the pyroxenes implies that the pyroxenes are more Mg-rich than the other minerals including the olivines, amorphous olivines, and amorphous pyroxenes. The PUMA-1 flyby measurements of comet P/Halley also indicated an overabundance of Mg-rich pryoxenes compared to olivines. Comet Hale-Bopp's pyroxenes are similar to pyroxere IDPs from the ’Spray‘ class, known for their D-richness and their unaltered morphologies: Hale-Bopp's Mg-rich pyroxenes may be pristine relic ISM grains.