[BAA 00291] Asteroidal occultation of a bright star on 2007 June 23/24

[Rick]

BAA electronic bulletin No. 00291 - http://www.britastro.org/

At around 00:19 UT (01:19 BST) on the night of June 23/24 (Saturday/Sunday), the Minor Planet (502) Sigune is predicted to occult the 4.9 magnitude star HIP 89918 (74 Oph), as seen from parts of the UK.  Occultations of naked-eye stars as seen from the UK are very rare but are potentially easy to observe with binoculars and small telescopes.

The predicted shadow track of this 16km size asteroid is due to cross Lincolnshire, the south Midlands and SE Wales.  However, as is frequently the case, there is significant uncertainty in the prediction and the one standard deviation (1SD) limits encompass much of northern, central, and south western England, and Wales.  For details, please see the chart on the European Asteroidal Occultation Network (EAON) website:

http://astrosurf.com/eaon/Cartes/06%20Juin/24%20Sigune.gif

The maximum expected duration of the occultation, for observers on the centre line, is only 1.2 seconds, but the faintness of the asteroid, mag 14.4, will ensure that the occultation is complete.

The star will be well placed at an elevation of about 40 degrees, almost due south. The Sun will be around 13 degrees below the horizon, so twilight will not be a problem. (Figures based on northern England.)  A star chart is included on the EAON chart, but Planetarium software may give a better view.

Owing to the uncertainty, observers should observe at least from 01:17 to 01:21 BST.  It has to be said that the probability of seeing a positive event from any particular location within the area is not more than 1 in 10. But if widely spread observers within the area attempt the occultation, the chances of one or more positive observations will be much enhanced. Negative results may be useful to pin down the actual track.  N.B. track shifts can exceed 1SD so observers should not be disappointed with a negative result!  And those outside the 1SD track may also wish to give it a
try.

Serious timings of the disappearance and reappearance, to an accuracy of around 0.1 seconds, should be sent to the undersigned using the standard format illustrated at:

http://astrosurf.com/eaon/Report%20form.htm

Clear skies and Good luck!

Andrew Elliott

Assistant Director (Occultations), Asteroids and Remote Planets Section
Email:  ae at f2s com

[Rick]

BAA electronic bulletin No. 00292 - http://www.britastro.org/

Asteroidal occultation of a bright star on 2007 June 23/24 - update

Just as the text for electronic bulletin 00291 was written, a last minute update was published showing a slight north shift of the occultation track and a narrowing of the confidence limits.  There is no significant change to the predicted time of the occultation.  This bulletin replaces 00291.

At around 00:19 UT (01:19 BST) on the night of June 23/24 (Sat/Sun), the Minor Planet (502) Sigune is predicted to occult the 4.9 magnitude star HIP 89918 (74 Oph), as seen from parts of the UK.  Occultations of such bright stars are a rarity but easy to observe with binoculars and small telescopes.

The main track now crosses Central Yorkshire (near the adjacent borders of all four 'Ridings'), Greater Manchester, Cheshire, and parts of north Wales.  The probability of seeing an occultation from any site within this track has risen to around 20%.  The 1 standard deviation path extend southwards from NE England, north Yorkshire and Lancashire, to a line running from the Humber estuary, through the north and central midlands, to central south Wales (probability 9%).  For details, please see the updated chart on the European Asteroidal Occultation Network (EAON) web site:

http://astrosurf.com/eaon/Cartes/06%20Juin/24%20Sigune.gif

There is also a more detailed 'station map' generated by Oliver Klös at:

http://www.euraster.net/maps/20070624-Sigune_oke.gif

The maximum expected duration of the occultation, for observers on the centre line, is only 1.2 seconds, but the faintness of the asteroid, mag 14.4, will ensure that the occultation is complete.

The star will be well placed at an elevation of 40 degrees, almost due south. The Sun will be around 13 degrees below the horizon, so twilight will not be a problem. (Figures based on northern England.)  A star chart is included on the EAON chart, but Planetarium software may give a better view.

As before, observers should observe for at least two minutes either side of the central time quoted above.  If widely spread observers within the area attempt the occultation, the chances of one or more positive observations will be much enhanced.  Negative results may be useful to pin down the actual track.  N.B. track shifts can exceed 1SD so observers
should not be disappointed with a negative result!  And those outside the 1SD track may also wish to give it a try.

Serious timings of the disappearance and reappearance, preferably to an accuracy of around 0.1 seconds, should be sent to the undersigned using the standard format illustrated at:

http://astrosurf.com/eaon/Report%20form.htm

Good luck!

Andrew Elliott

Assistant Director (Occultations), Asteroids and Remote Planets Section
Email:  ae at f2s com
BAA ARPS website: http://homepage.ntlworld.com/roger.dymock/index.htm