A possible plasma jet in Comet Hale-Bopp

Pergamon

A translation

1998

Chin. Astron. Astrophys. Vol. 22, No. 1, pp. 99-100, of Acra Astron. Sin. Vol. 17, No. 4, pp. 435-436, 0

1998 Elsevier

Science

B.V.

All rights

Printed 0275.1062/98

1997

reserved

in Great $19.00

Britain. + 0.00

PII: SO2751062(98)00014-9 Brief

Report

A possible

plasma jet in Comet

Hale-Bopp

t

ZHAO Jun-liang QIAN Bo-then TANG Yuan TAO Jun GU Min-feng Shanghai

Observatory,

Chinese

Academy

of Sciences,

Shanghai

200030

Abstract A large plasma jet of Comet Hale-Bopp was observed in the B band on 1996-09-11 with the 1.56-m telescope and a Series 200 CCD camera. Key

words:

On 1996-09-11,

comet

Hale-Bopp-plasma

we observed

jet

a huge jet in Comet

Hale-Bopp

using our 1.56-m telescope

and

a Series 200 CCD camera. Because the jet was seen only in the image taken through the B filter, and not in those through the V and R filters, we think it is a plasma jet. The apparent size of the comet at the time was large, so we used a focal reducer, reducing the original focal length by a factor of 3, to f = 522.5 cm, and 1 pixel= 0.75”. We obtained a total of 7 CCD frames (the observing log is given in Table 1). The images were treated with the IRAF software package: we first used IMCOPY to cut out a 4Opixx40 pix area near the comet that included a faint star for reference, then we used CONTOUR to draw the contour lines at steps of 20 counting units. Fig. 1 is the contour map in the B band. We see that the contours of the comet to be composed of a core and a jet. On the lower right is the star with circular contours, while the comet on the upper left shows the contours of two inter-connected, flattened circles. Obviously, the left one is the comet; the right one could be due to one of three causes: 1) it is another image of the comet caused by telescope jitter, 2) there happens to be another star at the location, or 3) it is a jet ejected by the come. Possibility 1 seems to be ruled out by the absence of any other double images, in fact the single, very circular image of the star implies good tracking of the telescope. As regards 2, if it is just another star at the location, then the same star should show up in the images through the other filters taken within a few minutes of this one (for the motion of the comet was very slow), but this is not the caSe (see Fig. 2). Hence, we say there is only one possibility;-a jet. This jet is located about 4.5 arcsec north of the comet, and its peak value is 80% that of the comet, as judged from the contour map; thus, it is a very large jet. t Supported Received

by National 199&O%23;

Natural revised

Science version

Foundation 1997X13-25

99

100

ZHAO

Table Number

1

Jun-liang

et al.

Observation Log-file

Start Time (BT)

Exposure Time

h:m:s

8

1

19:01:51

45

2

19:11:28

45

R

3

19:14:41

45

R

4

19:17:26

240

V

5

19:31:38

240

V

6

19:39:11

240

V

7

19:56:17

300

B

Fhmes

Filter

R

This jet is not seen on the V and R images taken on the same night, but these images do show clearly two dusty jets. The V contours dashed.

We see that the plasma jet (shown

dusty jets (shown solid);

are shown solid in Fig. 2 and the B contours, dotted)

d oes not coincide

with either of the

rather, it falls between the two.

N-

Fig. 1

The contour of comet Hale-Bopp in B band

Because of weather conditions the question

The combined in V (solid)

our 1.56-m telescope

images during the time, and Beijing and Yunnan are now considering

Fig. 2 Hale-Bopp

of removing

contours

of comet

and B (dashed)

band

was unable to take more usable B

Observatories

also failed to secure any. We

the light of the comet from the jet.