Lucky Star -projekti lähestyi Ursaa tiedotteella Hektor-asteroidin tähdenpeitosta, joka voisi näkyä Suomen alueella. Projekti tutkii pääasiassa kaukaisempia asteroideja, mutta Jupiterin trojalaisen asteroidin Hektorin muodon tutkimukset tehdään projektin yhteydessä. Tähdenpeitot ovat tärkeä keino hahmottaa asteroidien kokoa.
Hectorin aiheuttama 12,5 mag tähden peitto on hiukan marginaalinen Suomessa. Tämän hetken ennusteen perusteella näkymisalue on Ahvenanmaalla, Turun saaristossa ja Hankoniemellä. Epävarmuusalue ulottuu kuitenkin laajemmin Lounais-Suomeen sekä läntiselle Uudellemaalle. Hektor ja peittyvä tähti ovat melko matalalla lännessä. Havainnot ovat kuitenkin tärkeitä haasteista riippumatta.
Ohessa lisätietoa:
My name is Damya Souami. I am a postdoctoral researcher in Astronomy at the Observatory of Paris-Meudon.
I am emailing to alert you about a stellar occultation event on Oct. 28th (night of the 27th to the 28th) by the large irregular trojan (624) Hektor.
This is an occultation of 12.5 mag star by the large trojan (624) Hektor on October 28th around 02:44 UT (night from Tuesday 27th to Wednesday 28th). In addition to the US, the path is favourable in south Finland, parts of Sweden, Norway, Estonia, Latvia, and even western Russia.
You are on the path of the event.
The maximum expected duration is of 14.2 sec. The expected drop is 2.0 mag.
The J2000 position of the star is:
RA : 00h35m01s8877 J2000
DEC : +18d14m08s599 J2000
Observations are requested on Oct. 28th, from 02h30 to 03h00 (UT).
More information about the event is available here
https://lesia.obspm.fr/lucky-star/occ.php?p=41029.
I am attaching to this email the instructions file which can also be found here
https://share.obspm.fr/index.php/s/38o2dCt4CB4LsZX.
Please, note that in our group all observers are considered as collaborators and therefore co-authors to the scientific paper.
Please, let me know if you are equipped for the observation and if you are going to attempt the observation. Do not hesitate to email me if you have any questions.
I would really appreciate if you could forward this to other observers you might know. A good coverage of this event would help us constrain the 3D shape model of this irregular (possibly bilobed) object.
Cheers,
Damya
This campaign is carried out under the "Lucky Star" umbrella. Lucky Star is an EU-funded research activity that agglomerates the efforts of the Paris, Granada and Rio teams. So you may be contacted by different people from these three groups, but we are all working together. See Lucky Star web page for details:
http://lesia.obspm.fr/lucky-star/
Observation protocol for the stellar occultation
by (624) Hektor on Oct 28th, 2020RationaleThis observational campaign is carried out under the "Lucky Star" umbrella. Lucky Star is an
EU-funded research activity that agglomerates the efforts of the Paris, Granada and Rio teams.
Several people from these three groups may contact you, but we are all working together.
See the Lucky Star web page for details:
http://lesia.obspm.fr/lucky-star/.
This campaign aims at the physical characterisation of (624) Hektor which is the largest Jupiter
trojan. Hektor is an elongated irregular body. This study aims at refining the shape and size
model of Hektor, and determining its density with a better accuracy.
Event informationThis is an occultation of 12.5 mag. star by the large trojan (624) Hektor on October 28th around
02:44 UT (night from Tuesday 27th to Wednesday 28th). In addition to the US, the path is
favourable in parts of Sweden, Norway, Estonia, Latvia, and even western Russia.
The maximum expected duration is of 14.2 sec. The expected drop is 2.0 mag.
The J2000 position of the star is:
RA : 00h35m01s8877 J2000
DEC : +18d14m08s599 J2000
Observations are requested on Oct. 28th, from 02h30 to 03h00 (UT).
More information about the event is available here
https://lesia.obspm.fr/luckystar/occ.php?p=41029. An interactive finding chart is also available on this page, just click on
‘link to sky-map’.
Exposure TimeThis event may last up to 14.2 seconds so long exposure times up to a couple of seconds are
possible. As the occulting object is very dim, the target star will "disappear", so even if the
target star looks very dim in the images, we will be able to measure the event, we don't need
high signal to noise. These on/off events make the detection and determination of the correct
ingress/egress times strait forward, by modelling the light-curve. The most important thing is
to have good enough time resolution without have too short exposure time. It is important to
have short readout time.
Beware of the dead time between the images: if you manage an exposure time of 1 second (for
example), but your camera takes 2 sec to read the image, then there is a 67% chance that you
miss the disappearance/reappearance of the star [chance of missing = 1 - {1/(1+2)}].
It is thus better to have, for example, 4 sec integration, so you have 67% chance to get the
occultation in one of your exposures [chance of getting = 4/(4+2)].
To reduce the readout time, and data size: please, window the FOV (if possible), and using a
binning 2x2 for example. Note that it is better to have all the star flux in 3 or 4 pixels than
oversample the seeing. The benefits of it are the faster readout, smaller file size and better
photometry.
Absolute time accuracy is essential: to connect all the observations together after the fact. Check
the time of your computer with reliable sources. It is advised to check the registered time right
after and right before the integrations, so if there is a drift, we can correct it by having the
difference.
Apps such as Astro Flash Timer (for Apple) or Occult Flash Tag (for Android) can be used to
check your times:
https://occultations.org/observing/software/. If you need to use NTP, please
read this article to get the best of it:
http://www.iotaes.de/JOA/JOA2020_2.pdf.
After the observation:Please take darks. Cover your telescope to avoid any light contamination, and take a dozen
frames with the same exposure time used to acquire data.
If possible, take flats. Make an evenly illuminated target (with a board, back illuminated
white sheet), and take "white" images avoiding saturation.
Please, download the following form
https://share.obspm.fr/index.php/s/8oJGjjYBxzNMbeD,
complete it and email it to me along with your data as well as your preliminary light-curve (if
you have any).
You can upload the data to your own drive (dropbox, google drive, … ) and send me the link,
use transfer data platforms or ‘drop of the data’ here
https://zendto.obspm.fr/changelocale put
my name and email address Damya Souami damya.souami@obspm.fr.
Policy of our group:All observers are considered as collaborators to the scientific project, and therefore co-authors
to the paper.
Contact
If you need any further assistance, you can contact us through these addresses:
- Damya Souami damya.souami@obspm.fr;
- Felipe Braga Ribas ribas@on.br;
- Josselin Desmars josselin.desmars@obspm.fr;
- Jose-Luis Ortiz Jose Luis Ortiz ortiz@iaa.es;
- Sicardy Bruno bruno.sicardy@obspm.fr;
- Pablo Santos Sanz psantos@iaa.es
Clear skies to all!
Tuoreimmat viestit
