Near-infrared brightness of the Galilean satellites eclipsed in Jovian shadow TSUMURA Kohji (FRIS, Tohoku Univ.)

Transcription

1 Near-infrared brightness of the Galilean satellites eclipsed in Jovian shadow TSUMURA Kohji (FRIS, Tohoku Univ.) Collaborators: Shirahata M., Minowa Y., Hayano Y.(NAOJ), Arimatsu K.(Univ.of Tokyo), Takahashi Y. Kuramoto K. (Hokkaido Univ.) Nakamoto T. (Tokyo Tech.) Wada T., Matsuura S. (ISAS/JAXA) Nakajima K. (Kyushu Univ.) Kimura J. (ELSI, Tokyo Tech) Honda C. (Univ.of Aizu) Egami E (Arizona Univ.) Jason Surace (Caltech) Jupiter IRCS+AO188 (JHK) 2012/Jul./21

2 (Original) purpose of the observation Observations of Cosmic Infrared Background (CIB) to study star formation at the early universe. SKY brightness = Zodiacal light (ZL) + Galactic light + CIB Zodiacal light is the strongest foreground radiation Biggest error source. CIB observation without ZL subtraction error using Galilean satellites as occulters. Satellite in eclipse ZL Surrounding sky ZL+CIB

3 Eclipse of Galilean satellites Galilean satellites: Jovian moons Io, Europa, Ganymede, Callisto Io is not suitable owing to volcanoes Jupiter Galilean satellites The moons are shielded in Jovian shadow Two observable chances in a year Io 1.76 days Europa Ganymede 3.55 days 7.16 days Callisto days Observable seasons Earth Sun Earth

4 Europa Europa zoom-in Ganymede Jupiter

5 Straylight from Jupiter Straylight control is very important Scattered Jovian light at the earth atmosphere Scattered Jovian light in the optics CH4-long band reduces Jovian stray light Europa Ganymede Callisto Straylight brightness relative to sky

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7 Special tracking method Movement of objects Target : Europa eclipse Telescope track: Jupiter AO guide: Ganymede All of them are nonsidereal Thanks to Subaru SAs for success of such a difficult observation IRCS FoV (Juputer Track) Europa in eclipse Ganymede (AO guide) Jupiter

8 Bright in shadow! Ganymede and Callisto are bright in Jovian shadow 10-6 of its out-of-eclipse brightness New discovery of Subaru and HST Ganymede in eclipse by HST Callisto in eclipse by Subaru

9 Europa eclipses Instrument Date Band Depth Result Subaru/IRCS 2012/2/21 J-band (1.25µm) ~0.5 Non-detection <1.5 µjy HST/WFC3 2013/5/5 F139M (1.39µm) Non-detection <5.5 µjy Subaru/IRCS 2013/11/19 CH 4 -long band (1.69µm) >0.4 Non-detection <88 µjy (Bad weather) HST/WFC3 2014/3/26 F139M (1.39µm) µjy Ganymede eclipses Instrument Date Band Depth Result Spitzer/IRAC 2012/3/26 Ch.-1 (3.6 µm) >0.87 Non-detection <3.6 µjy Subaru/IRCS 2012/7/26 J-band (1.25µm) µjy HST/WFC3 2013/2/5 F160W (1.60µm) µjy HST/WFC3 2013/3/5 F139M (1.39µm) µjy Spitzer/IRAC 2013/4/17 Ch.-1 (3.6 µm) >0.67 Non-detection <3.6 µjy Spitzer/IRAC 2013/4/24 Ch.-1 (3.6 µm) >0.67 Non-detection <3.6 µjy Callisto eclipses Instrument Date Band Depth Result Subaru/IRCS 2013/10/19 J-band (1.25µm) µjy

10 Why were they bright in eclipse? Hypothesis discussed here 1) Jovian aurora and/or lightning 2) Illumination from other satellites 3) Emission from the satellites in eclipse 4) Refracted sunlight in Jovian atmosphere 5) Scattered sunlight by hazes in Jovian atmosphere

11 Hypothesis : 1), 2) 1) Jovian aurora/lightning Europa, nearest to Jupiter, should be brightnest 2) Illumination from other satellites Walter Myers One detected event (Europa) can be explained. Detected brightness in other events cannot be explained Io Europa Jupiter

12 Hypothesis: 3) 3) Emission from the satellites Ganymede aurora emission is localized It cannot explain our detected flat brightness McGrath+ (2013) Atmospheric emission from the satellites cannot explain the detected SED. Assuming OH dominated airglow.

13 Hypothesis: 4) 4) Refracted sunlight in the atmosphere Galilean satellites should be brighter only by refraction effect. Refraction in the Jovian atmosphere

14 4) Refracted sunlight in the atmosphere Galilean satellites should be brighter only by refraction effect. Absorption by dusts in the atmosphere (eg. Smith 1980) Hypothesis: 4) Dust absorption

15 Hypothesis: 5) 4) Refracted sunlight in the atmosphere Galilean satellites should be brighter Dust absorption 5) Scattering by hazes at higer atmosphere (First observational detection of Jovian hazes.) Scattering by hazes

16 Jovian atmosphere modeling Previous studies investigated ~100mbar range by observations of ingress/egress (e.g. Smith et al.1980) Scattering at higher range (~10mbar) is required There are less information about this pressure range. Important range for haze particle generation. Observational study of Jovian upper atmosphere by ground based observations of eclipses. Jovian atmosphere Gas layer Haze layer 2 Haze layer 1

17 Application to Exo-planet transit Atmosphere around exoplanets are observed by transit. Little information about transmission spectrum of planetary atmosphere in our solar system. This method provides us the transmission spectrum of Jovian atmosphere Standard for classification of exoplanet atmosphere Transit observation of Exo-planet Star Sun Planetary atmosphere Exo-planet Galilean satellite eclipse observation Jovian atmosphere Earth Jupiter Earth Galilean satellite 国立天文台岡山天体物理観測所 Web リリース (2013 年 6 月 ) 晴天のスーパーアース? 低質量の太陽系外惑星 GJ3470b の大気を初めて観測

18 Current Status Two eclipses (Callisto and Ganymede) were observed in S14B by Gemini/NIRI (Time exchange program) Bad weather and some troubles. Unknown stray light Two eclipses (Callisto and Ganymede) will be observed in S15A by Subaru/IRCS and Gemini/NIRI (Time exchange program)

19 Summary Deep imaging of Galilean satellite eclipses in Jovian shadow by Subaru, Hubble, and Spitzer. Ganymede, and Callisto were bright even in the Jovian shadow at around 1.5 um. Ganymede: 4e-6, Callisto: 2e-6 relative to their brightness out of eclipse. Ganymede was under detection limit at 3.6 um. Thermal radiation from their 120K surface is neglgible. Europa is much darker than the others. What is the light source? Forward scattering of sunlight at Jovian upper atmosphere. We can investigate hazes in the Jovian upper atmosphere by ground-based observations.

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21 Light curve Brightness depends on the satellite position Impact Parameter Jovian shadow satellite 衛

22 あるモデルパラメータでの計算結果