the b-v colors and photometric variability of nix and hydra, pluto’s two small satellites
DESCRIPTION
The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites Max Mutchler (STScI) S. Alan Stern (SwRI) Hal Weaver (JHU/APL) Andrew Steffl (SwRI) DPS Meeting in Pasadena 11 October 2006. Overview. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/1.jpg)
The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites
Max Mutchler (STScI)S. Alan Stern (SwRI)Hal Weaver (JHU/APL)Andrew Steffl (SwRI)
DPS Meeting in Pasadena11 October 2006
![Page 2: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/2.jpg)
Overview
• HST obs: 4 epochs in V-band, different detectors/strategies, B filter for last, pre-covery
• Show images: data quality, photometric issues (spikes, PSF halos, artifacts)
• Describe photometry: apertures, corrections, etc.
• Photometric results: neutral, no variability• Publications, future work, NH!
![Page 3: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/3.jpg)
Hubble ACS Hubble ACS observations observations of Nix and Hydraof Nix and Hydra
• 15 May 2005: WFC, discovery!, V-band
• 18 May 2005: WFC, preliminary orbits, V-band
• 15 Feb 2006: HRC, confirmation, V-band
• 2 March 2006: HRC, B and V-band (B-V colors)
• Pre-discovery HRC detections in 2002-2003 (Buie et al.)
• Merge this with actual images?
![Page 4: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/4.jpg)
North-up images from each epoch
• 6.4 x 6.4 arcseconds (compact system)• Short exposures: Pluto-Charon unsaturated• Long exposures: Nix and Hydra detected• ACS / WFC: longer exposures (fishing), gap• ACS / HRC: less saturation of Pluto-Charon• Nix & Hydra not optimally placed in every frame
(background stars, diffraction spikes, bright Pluto-Charon PSFs): only use ideal frames
• Images provide sense of data quality, photometry hazards…
![Page 5: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/5.jpg)
15 May 2005, ACS / WFC V-band, median 4 long exposures
![Page 6: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/6.jpg)
15 May 2005, ACS / WFC V-band, median 4 long exposures
![Page 7: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/7.jpg)
15 Feb 2006, ACS / HRC V-band, drizzle 4 long exposures
![Page 8: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/8.jpg)
2 March 2006, ACS / HRC V-band, drizzle 3 long exposures
![Page 9: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/9.jpg)
2 March 2006, ACS / HRC B-band, drizzle 3 long exposures
![Page 10: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/10.jpg)
Pre-discovery HRC observations
• Hubble program by Buie & Young, 2002-2003
• Primarily designed to map surface features (albedo) of Pluto and Charon
• New moons marginally detected
• Good orbit determination• Photometry implied Nix
reddish (B-V=+0.91), like Pluto (B-V=+0.00) and Hydra neutral (like Charon) (Buie et al. ???)
![Page 11: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/11.jpg)
Photometry• ACS filters: F606W “broad V”, F435W “Johnson B”• Short and long exposures (moons 5000x fainter than Pluto-Charon)• Hazards: diffraction spikes, PSF halos, artifacts…• Measurements on 3 of 4 dates for each satellite• Aperture phot? Aperture used?• Aperture corrections, CTE effect (WFC edge! PSFs help fill traps)• Adjust for changing heliocentric/geocentric distances, and solar
phase angle (assume Charon’s phase law)• Instrumental magnitudes (Sirianni et al. 2005)• Uncertainty: background, PSFs, CTE?• Hydra (P1) variation: 1.00 : 0.78 : 0.73• Nix (P2) variation: 1.00 : 0.79 : 0.86 (put in table?)• Limiting magnitudes (Steffl): V=26.8 (90% confidence level);
diamiter limits 10-40 km
![Page 12: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/12.jpg)
• IAU Circular 8686 (at left)• Stern et al., AJ (submitted),
astro-ph/0605014• Both have neutral (grey)
reflectivities, like Charon • Similar origins (collision event) for
all 3 moons• No strong photometric variability• Both towards larger end of
allowable sizes (over ~100 km)?• Lower albedos than Charon?• No other satellites of similar size, to
limiting magnitude V=26.8, 90% confidence (Steffl et al. AJ) Photometric
results for Nix & Hydra
![Page 13: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/13.jpg)
Hubble ACS photometry
DateNix
(S/2005 P2)
Hydra
(S/2005 P1)
15.05 May 2005 V = 23.41 +/- 0.15 V = 22.96 +/- 0.15
18.14 May 2005V = 23.41 +/- 0.15 V = 22.96 +/- 0.15
15.66 Feb 2006 V = 23.7 +/- 0.2 V = 23.26 +/- 0.15
2.75 March 2006 V= 00.0 +/- 0.0B-V = +0.654 +/- 0.065
V= 00.0 +/- 0.0B-V = +0.653 +/- 0.026
Charon B-V=0.710 (from Buie et al., 1997, Icarus, 125, 233)
![Page 14: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/14.jpg)
Team is planning more elaborate observations inJuly 2015…
![Page 15: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/15.jpg)
Publications
• IAU Circulars 8625, 8676, 8686
• Weaver et al. 2006, Nature• Stern et al., 2006, Nature• Steffl et al., 2006, ApJ• Stern et al., 2006, AJ,
submitted
![Page 16: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/16.jpg)
Hubble ACS astrometry(Pluto-centric, center of light)
DateNix
(S/2005 P2)
Hydra
(S/2005 P1)
15.05 May 2005d = 2.09 +/- 0.035 arcsec
PA = 326.9 +/- 0.5 deg
d = 1.85 +/- 0.035 arcsec
PA = 264.2 +/- 0.5 deg
18.14 May 2005d = 2.22 +/- 0.035 arcsec
PA = 355.5 +/- 0.5 deg
d = 2.36 +/- 0.035 arcsec
PA = 305.8 +/- 0.5 deg
15.66 Feb 2006d = 2.03 +/- 0.010 arcsec
PA = 355.3 +/- 0.3 deg
d = 2.86 +/- 0.010 arcsec
PA = 343.0 +/- 0.3 deg
2.75 March 2006d = 1.43 +/- 0.015 arcsec
PA = 213.7 +/- 0.5 deg
d = 2.69 +/- 0.015 arcsec
PA = 138.2 +/- 0.5 deg
* Confirmed orbital solution from Buie et al., 2005
![Page 17: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/17.jpg)
The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites
Max Mutchler, Alan Stern, Hal Weaver, Andrew Steffl
Pluto’s two small satellites, Nix and Hydra, were observed on four dates (15.1 and 18.1 May 2005, 15.7 February 2006, and 2.8 March 2006) using the Hubble Space Telescope’s (HST) Advanced Camera for Surveys (ACS). V-band magnitudes were obtained for all dates, and B-band magnitudes were additionally measured on the last date.
We find that both satellites have essentially neutral (grey) reflectivities, like Charon. We also find that neither satellite exhibited strong photometric variation, which might suggest that Nix and Hydra are toward the large end of their allowable size range, and therefore may have lower albedos than Charon.
Support for this work was provided by NASA through Grants GO-10427 and GO-10774 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc.,and the New Horizons Pluto-Kuiper Belt mission.
![Page 18: The B-V colors and photometric variability of Nix and Hydra, Pluto’s two small satellites](https://reader036.vdocuments.net/reader036/viewer/2022062315/56815152550346895dbf75db/html5/thumbnails/18.jpg)
Division for Planetary Sciences of the
American Astronomical Society
http://www.aas.org/~dps/dps.html