Jupiter s Galilean satellites mutual events as a teaching tool.

Transcription

1 Jupiter s Galilean satellites mutual events as a teaching tool. J.F. Rojas & A. Sanchez-Lavega EPSC 2015 Nantes

2 Introduction The Aula Espazio Gela (AEG) was created at UPV/EHU to promote the study and research in astrophysics, planetary science and space technology. To accomplish this: The AEG Observatory, atop the building of the Engineering school. The Master of Space Science & Technology. [ A. Sánchez-Lavega et al., The Aula EspaZio Gela and the Master of Space Science & Technology in the Universidad del País Vasco (University of the Basque Country, European Journal of Engineering Education, 39, (2014) ] The text below describes a possible work to be performed as a master thesis. It intends that the student gain expertise in: Acquairing and using photometric data and preparing light curves. Astrodynamics, to establish the relation of the orbital parameters of the Galilean satellites with the light curves. Obtaining the sizes or albedos of the Galilean satellites. EPSC 2015 Nantes 1

3 What is a phemu Two times per Jupiter orbit both Earth and Sun cross the Jovian Equatorial plane. At these moments mutual occultations and eclipses of the Galilean satellites can happen. Geometry imposes severe restrictions on the phenomena. We can use these events to obtain data about positions, sizes and albedos. [ J.E. Arlot et al. A&A 572, A120 (2014) ] [ X-L Zhang & Z. Liu Research in Astron. Astrophys vol. 11 No 10 ] Two possibilities: Eclipse: The shadow of a satellite is projected over another satellite. Occultation: The disk of a satellite appears projected along our line of sight over the disk of another satellite. EPSC 2015 Nantes 2

4 What is a phemu During an occultation the amount of light changes: changes in the total visible reflecting surface difference in albedos To the SUN During an eclipse the amount of light also changes: different irradiance on every point of target complicated by the solar limb darkening eclipse EPSC 2015 Nantes 3

5 Measurement procedure Telescope Celestron C-11 + CG5 mount aperture: 280 mm focal length: 2800 mm Barlow lens: 2X Detector Imaging Source DMK-21 AU618AS resolution: 60 fps 600 nm 8 bit no filter Material from Aula Espazio Gela Images The software of this camera (ICcapture) produces a monochrome video that is saved on a computer using an Y800 codec (no compression). The video files are.avi sequences of still frames. They do not include acquisition info at all. There is some time interval between videos. EPSC 2015 Nantes 4

6 Measurement procedure Procedure for every video: Extract all the frames. For every frame: Place the photometric areas over target. Place the photometric areas over reference (if available). Determine signal and background for both objects. Save the data. Repeat procedure with next frame. Repeat procedure with next video. We lack the real time of every frame. It should be obtained from the time of the full video taking account of the selected frame rate (conditioned by exposure time). PhotoRegions: developpped to automatically accomplish all these tasks. EPSC 2015 Nantes 5

7 PhotoRegions interface Measurement procedure EPSC 2015 Nantes 6

8 Measurement procedure Signal = Total DN - (Npixels X mean background DN) To standardize results we calculate normalized ratios: Io Ganymede + Europa If reference available, to have a cleaner signal: target / reference ratio; then normalize. If no reference: ratio of measured values to the wings mean values of the same object. EPSC 2015 Nantes 7

9 Computer simulation We developed computer simulations of both phenomena to gain knowledge of the physical meaning of our measured results. Occultation: The disk of a satellite of radius R2 and mean geometric albedo a2 moves over the disk of another satellite (the target) of radius R1 and mean geometric albedo a1. The minimum distance between their centers is S (the impact parameter) [parameters from IMCCE web]. As we lack high precision ephemeris of the phenomenon we only can obtain the value of S that matches our measured data. The start and end times that we get of our simulation are not reliable. Eclipse: Radii and S as in occultation. We use external data from NASA Eyes tool such as Jupiter Sun and satellite1 satellite2 distances at the relevant time. We calculate angular sizes of the Sun and of satellite 2 from the satellite 1 position. EPSC 2015 Nantes 8

10 Computer simulation For every point on the surface of the disk of satellite 1 (target) we calculate the light incoming from an element of the apparent surface of the Sun disk, taking account of limb darkening [ D. Hestroffer & C. Magnan A&A 333, (1998) ]. Of course that points that are hidden by the satellite 2 do not contribute. Results again cannot predict times because of the lack of ephemeris. EPSC 2015 Nantes 9

11 Results analysis Few observations: cloudy weather, problems with time registration on the laptop. Reported events (IMCCE ephemeris): Date begin (UT) end (UT) event type frames 2015/02/09 20:56:05 21:01:29 3O /12/24 06:24:22 06:45:44 2E /02/09 21:06:06 21:13:20 3E /04/11 21:01:07 21:06:31 1E Some image series of very high quality. Ganymede 1.32 EPSC 2015 Nantes 10

12 DN3 / DN2 normalized Results analysis DN1 / DN3 normalized DN3 / DN1 normalized Actual measurements sometimes become very noisy! Filtering required. EPSC 2015 Nantes 11

13 As a teaching tool DN1 / DN3 normalized DN1 / DN3 normalized Fitting a model to the results: (admitting relative velocity is constant) expected fitted impact param. (km) relative vel. (km/s) expected fitted impact param. (km) relative vel. (km/s) There is some asymmetry. EPSC 2015 Nantes 12

14 As a teaching tool DN3 / DN1 normalized DN3 / DN2 normalized expected fitted impact param. (km) relative vel. (km/s) expected fitted impact param. (km) relative vel. (km/s) This dataset is very noisy. EPSC 2015 Nantes 13

15 As a teaching tool Summary of results: Date begin end event frames flux drop flux drop flux drop S (km) S (km) (UT) (UT) (IMCCE) modelled measured model. meas. 2015/02/09 20:56:05 21:01:29 3O Date begin end event frames flux drop flux drop flux drop S (km) S (km) radius (km) ap diam. (') distance (km) (UT) (UT) (IMCCE) modelled measured model. meas. umbra penum. Sun satel. sat-sat to Sun 2014/12/24 06:24:22 06:45:44 2E E /02/09 21:06:06 21:13:20 3E E E /04/11 21:01:07 21:06:31 1E E E+8 These observations will be sent to the IMCCE to contribute the astrometric studies of Galilean satellites by means of mutual events. EPSC 2015 Nantes 14