C / 2004 F4 (Bradfield)

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C / 2004 F4 (Bradfield) [i]
Bradfield.JPG
Properties of the orbit ( animation )
Epoch:  June 1st, 2004 ( JD 2,453,157.5)
Orbit type long-period
Numerical eccentricity 0.99929
Perihelion 0.168 AU
Aphelion 476 AE
Major semi-axis 238.2 AU
Sidereal period ~ 3,675 a
Inclination of the orbit plane 63.2 °
Perihelion April 17, 2004
Orbital velocity in the perihelion 102.7 km / s
history
Explorer W.A. Bradfield
Date of discovery March 23, 2004
Source: Unless otherwise stated, the data comes from JPL Small-Body Database Browser . Please also note the note on comet articles .

C / 2004 F4 (Bradfield) is a comet that could be seen with the naked eye in 2004 . Its flyby of the sun was also observed by the SOHO space telescope .

Discovery and observation

The comet was discovered on the evening of March 23, 2004 by the then 76-year-old "comet detective" William A. Bradfield in Australia with a 150 mm - f / 5.5 - refractor . It was his eighteenth comet discovery, almost nine years after his last. Bradfield estimated the comet's brightness to be about 8 mag. Bradfield was able to find it again the following evening, after which the comet was initially unobserved and the discovery was not reported to the International Astronomical Union (IAU) until March 28th .

It was two weeks before Bradfield found the comet on April 8th in the still bright twilight . After that he was also seen by other astronomers in the southern hemisphere .

After its discovery, the comet moved north and rapidly increased in brightness, so that it could be observed on April 9 with a magnitude of 5 mag and on April 12 with 3.3 mag and a tail length of 2 ° . After that it disappeared for observers on earth, initially in the bright dusk.

On April 18, at 3:14 a.m. UT , the comet passed the Sun at an angular distance of only 2.6 ° . Just 4 days after the passage of the sun, the comet could already be observed again in the northern hemisphere in the morning sky . The brightness decreased again and dropped to 5.8 mag by the end of April. At this time the comet's tail had a length of 10 ° visually and 20 ° photographically .

At the end of April 2004, together with comet Bradfield, comet C / 2002 T7 (LINEAR) could also be observed at dawn in the eastern sky, shortly afterwards comet C / 2001 Q4 (NEAT) also appeared in the evening sky.

The position of Comet Bradfield could be determined until mid-September.

The comet reached a maximum brightness of 3.3 mag, making it one of the 30 brightest comets since 1935.

Scientific evaluation

After the first orbit calculations for the comet could be carried out, it became clear that the comet would cross the observation field of the SOHO space telescope for several days in April. From April 16 to 21, the comet's flyby could be observed with the LASCO C3 coronograph on board SOHO. The comet achieved a brightness of about -2 mag due to the forward scattering of the sunlight on the dust particles.

Several images of Comet Bradfield, taken around the time Earth crossed the comet's orbital plane (May 2/3), showed a radial structure in the comet's dust tail along with a short, sunward-pointing tip. The observations confirmed the peculiarity of a "neckline structure" (NLS) in the dust tail of a comet, which was theoretically derived only in 1977.

From April 24 to May 20, the comet could be observed together with the two comets C / 2001 Q4 (NEAT) and C / 2002 T7 (LINEAR) also with the Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite . Around May 5th, the interaction of a coronal mass ejection (CME) of the sun with the plasma tail of the comet NEAT as well as wave-like influences on the plasma tails of NEAT and LINEAR by fluctuations in the solar wind could be observed for the first time. The plasma tail of Comet Bradfield, on the other hand, remained undisturbed, presumably because at the time of the observation it was no longer near the equatorial plane of the Sun, as was the case for the other two comets.

In May 2004, observations of the 18 cm OH emission line at Comet Bradfield were made with the Nançay radio telescope .

Orbit

A relatively precise elliptical orbit could be determined for the comet from 248 observation data over a period of 147 days , which is inclined by around 63 ° to the ecliptic . At the point of the orbit closest to the sun ( perihelion ), which the comet last passed on April 17, 2004, it was only about 25.2 million km from the sun, in the area well within the orbit of the planet Mercury . On the same day, the closest distance to Venus was reached with about 91.1 million km , while the comet had already passed Mars on January 27 at a distance of about 107.1 million km. On April 18, it approached Mercury to about 38.8 million km and one day later on April 19, it came close to Earth to about 0.83  AU / 124.3 million km.

The comet moves in an extremely elongated elliptical orbit around the sun. According to the orbital elements afflicted with a certain uncertainty, its orbit some time before the passage of the inner solar system in 2004 had an eccentricity of about 0.99914 and a semi-major axis of about 195 AU, so that its orbital period was about 2710 years. The comet could therefore last have appeared in antiquity around the year -708 ( uncertainty ± 15 years). Due to the gravitational pull of the planets, in particular by passing close by Saturn on April 3, 2001 in about 5 ¾ AU and on Jupiter on April 24, 2001 in about 8 ½ AU, the orbital eccentricity was about 0.99929 and the semi-major axis to enlarged about 237 AU, so that its orbital period increased to about 3650 years. When it reaches the point of its orbit furthest from the sun ( aphelion ) around the year 3828 (uncertainty ± 12½ years) , it will be 70.8 billion km from the sun, almost 475 times as far as the earth and almost 16 times as far as Neptune . Its orbit speed in aphelion is only about 0.037 km / s. The next perihelion of the comet is expected to take place around the year 5652 (uncertainty ± 25 years).

See also

Web links

A variety of photographs of comet C / 2004 F4 (Bradfield) exist on the Internet. The following web links show only a small selection of them:

Individual evidence

  1. ^ Astronomical Society of South Australia: Comets Discovered from South Australia. Retrieved March 4, 2016 .
  2. ↑ DWE Green: IAUC 8319: C / 2004 F4. IAU Central Bureau for Astronomical Telegrams, accessed March 23, 2016 .
  3. ^ A b Gary W. Kronk's Cometography: C / 2004 F4 (Bradfield). Retrieved on May 5, 2014 (English, with many pictures of the comet).
  4. ↑ a b NASA JPL Small-Body Database Browser: C / 2004 F4 (Bradfield). Retrieved March 27, 2016 (English).
  5. ^ International Comet Quarterly - Brightest comets seen since 1935. Accessed March 4, 2016 .
  6. ^ SOHO: Comet Bradfield Coming into View (April 15, 2004). Retrieved March 26, 2016 (English).
  7. ↑ Sungrazer Project: Transits of Objects through the LASCO / C3 FOV in 2004. Accessed on March 26, 2016 (English).
  8. ↑ Y. Grynko: Light scattering by cometary dust particles with sizes large Compared to the wavelength of light. Copernicus GmbH, Göttingen 2005, ISBN 3-936586-37-3 .
  9. ↑ L. Pansecchi, M. Scardia: A neck-line structure in the dust tail of Comet C / 2004 F4 (Bradfield). In: Astronomy & Astrophysics. Vol. 430, 2005, pp. 1129–1132 doi: 10.1051 / 0004-6361: 20041766 ( PDF; 1.06 MB ).
  10. ↑ SMEI. Retrieved December 11, 2018 .
  11. ↑ A. Buffington, MM Bisi, JM Clover, PP Hick, BV Jackson, TA Kuchar: Analysis of Plasma-Tail Motions for Comets C / 2001 Q4 (NEAT) and C / 2002 T7 (LINEAR) Using Observations from SMEI. In: The Astrophysical Journal. Vol. 677, 2008, pp. 798-807 doi: 10.1086 / 529039 ( PDF; 1.03 MB ).
  12. ↑ TA Kuchar, A. Buffington, CN Arge, PP Hick, TA Howard, BV Jackson, JC Johnston, DR Mizuno, SJ Tappin, DF Webb: Observations of a comet tail disruption induced by the passage of a CME. In: Journal of Geophysical Research. Vol. 113, A04101, 2008, pp. 1–11 doi: 10.1029 / 2007JA012603 ( PDF; 419 kB ).
  13. ↑ The Nançay database of OH 18-cm lines in comets. Retrieved March 26, 2016 (English).
  14. ↑ A. Vitagliano: SOLEX 11.0. Archived from the original on September 18, 2015 ; accessed on May 2, 2014 .