Vermim in the sky

In the old days astronomers thought that asteroids were the vermim of the Solar System. Not any more, its satellites going around the Earth.

While observing for the transit of Gliese 581 b two weeks ago I managed to pick 13 satellites all parralel to each other going through the field (FOV 23'x23') over a period of 1 hour.

In fact I recorded 3 satellites parallel in one field alone. What is going on at RA 15h 19m, decl. -07d 43m? Why so such a concentration of satellites?

Eamonn A

Eamonn

I read some MPL posts recently on this subject - seems there are some RA/Dec locations teeming with satellites and are best avoided if you're taking long exposures. Alternatively, just take shorter exposures and bin those with satellites on...

How did you get on with the transit? Any luck?

Cheers
Dave

Dave

I actually had no choice as regards imaging that location becasue that is where the predicted transit of Gl 581 b was to occur. I sent the observations to Transit.org. It was actually an important observation because although the data showed no transit, it meant that the 'b' must have a lower inclination. Below is the report of the observation.

TRANSITS OF THE NEPTUNE-MASS PLANET ORBITING GL 581

The recent discovery of 'Earth like planet' GL 581'c' provides the incentive
of detecting a transit of Gl 581'b'

The detection of Gl 581'b' and may be 'c' planet
transit would have established the absolute mass of the
planet and its radius. From these parameters one could
also determine the mean density of the planet 'b' and also
estimate its chemical composition.

The 0.9m telescope at Kingsland Observatory, County Roscommon was used to monitor a possible transit.
Measurements of the light curves were between 22.40 hrs on May 4, 2007 and 0200 hrs
on 5 May, 2007. The uncertainty on the estimated mid-transit times was 86 minutes.

GJ 581 has a V mag of 10.56 and was strategically
placed on the CCD to include a suitable comparison star
in the frames. As comparison star one was located at a dis-
tance nearby. Anything as bright as 8 was avoided in case of descrepancies regarding the scintillation problem.

As check star a slighty fainter object (V = 12.2) was also located nearby.
There was a total of 230 images with 20s exposure times
was monitored over 3 hours with an average interval
of 12 seconds for each exposure. Practice runs were tried out with other stars at the meridian.
Exposure times were worked out with the right balance to avoid scintillation.

Photometric precision is therefore limited by scintillation and therefore selected a long exposure to get over this problem at 20 seconds. This also avoided any blooming from brighter stars.
MIRA PRO 7 programme was used that could achieve millimag accuracy of 0.001 in post processing for the 230 frames.

To determine whether or not a planet transit was present
in the data, it was important to have the estimated transit duration and
transit depth of GJ 581b. In turn an estimate of the
the radius of the planet, the radius of the star, the or-
bital separation between the two objects, and the orbital
period of the system. If it was an edge-on configuration (i = 90 deg) and a circular orbit,
the transit duration could have lasted between 85 to 100 minutes.
The observation therefore has ruled out transits of GJ581b
for very high inclinations. However, the star appears to
be more photometrically stable at short time scales than
at the time scale of months to years measured by Weis
(1994). Hence the 3.5 hours was sufficient for stability.
Longer monitoring may be required in order to catch the transit,
as the planet may now be at a lower inclination.

Eamonn A

Why so such a concentration of satellites?

In general, I think they are all up there, in some obscene quantity (when you take in the duds and the space junkets). It is just that in summer, with our night-time tilt to the Sun catching more ambient light, we will see far more satellites pass by. I am sick of counting them (and sometimes loosing count, as well as me cool! ).

Having not checked your co-ords for the object you're looking at/for, would it be above the horizon, or in a favourable position, during Winter (Nov/Dec/Jan)? That way, you would not have as many satellites crossing your FOV due to maximum darkness for our skies then.

:

Seanie.

We really noticed them in our Perseids watch last August, where in a relatively short time we'd clocked up over 30 satellite passes overhead in a couple of hours without even looking too hard.
I've seen some good potential captures ruined because of satellite passes.