IPB

Welcome Guest ( Log In | Register )

28 Pages V  « < 26 27 28  
Reply to this topicStart new topic
KBO encounters
JRehling
post Jul 10 2017, 07:37 PM
Post #406


Senior Member
****

Group: Members
Posts: 1968
Joined: 20-April 05
Member No.: 321



Per the non detection of the occultation, I haven't worked through the observers' math, but they stated clearly that they wouldn't know if they detected it right away, but only after analysis of multiple observers' data. This sounds like signal-to-noise is a/the relevant idea here. Remember, they weren't observing, say, Saturn occulting Regulus for a few minutes. This was a very, very small object occulting a very dim star, potentially very briefly, with error bars on time, space, and everything else. A given observer might have their telescope pointed right at the star when the occultation happens and still have insufficient SNR to know that they observed it. The numbers of photons we're talking about may be countable. And on top of this, they are earthbound observers looking through the atmosphere. I took video of *Vega* just to explore the effects of seeing/twinkling, and Vega varied by many tens of percents in brightness due to twinkling. CCDs have thermal/read noise. So of course this tiny occultation of a dim star is going to be a tough thing to know that you've detected. It doesn't mean that the telescopes were in the wrong place or the astrophysics are (necessarily) very different than expected. It means that they didn't see a signal through the noise and there are multiple non astrophysical factors that could contribute.
Go to the top of the page
 
+Quote Post
hendric
post Jul 10 2017, 09:48 PM
Post #407


Director of Galilean Photography
***

Group: Members
Posts: 832
Joined: 15-July 04
From: Austin, TX
Member No.: 93



Well, the stars are *fairly* bright, with V magnitudes of ~15.5 for the first two occultations, and 13.6 for the last one. Considering Pluto's V magnitude varies around the same range, it shouldn't be that difficult to detect with 16" telescopes.

The one wrinkle would be the integration time used on the images - shorter images give more accuracy for the start/end, and profiles, but less signal/noise.

Maybe twinkling helps with occultation measurements, since it spreads out the star's brightness over more pixels, similar to how Kepler uses an unfocused telescope. Then again, with the stars in this case fairly dim, and unlikely to saturate pixels, maybe concentrating the light is better. Twinkling shouldn't affect the total integrated brightness.

Sofia twitter claims to have successfully observed the shadow!

https://twitter.com/SOFIAtelescope


--------------------
Space Enthusiast Richard Hendricks
--
"The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke
Mother Nature is the final inspector of all quality.
Go to the top of the page
 
+Quote Post
Alan Stern
post Jul 19 2017, 02:45 PM
Post #408


Member
***

Group: Members
Posts: 493
Joined: 19-February 05
Member No.: 173



Success on the 17 July MU69 occultation! https://www.nasa.gov/feature/nasa-s-new-hor...ld-in-argentina
Go to the top of the page
 
+Quote Post
nprev
post Jul 19 2017, 05:07 PM
Post #409


Senior Member
****

Group: Admin
Posts: 7956
Joined: 8-December 05
From: Los Angeles
Member No.: 602



Amazing! The animated gif in the article clearly shows a gradual dimming and brightening...surely a demonstration of how small (and how slowly orbiting) MU69 really is given that it took observable time to occult an exceedingly small stellar disc.

Remarkable achievement, Alan, as per you & your team's usual. smile.gif


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
ngunn
post Jul 19 2017, 11:13 PM
Post #410


Senior Member
****

Group: Members
Posts: 3430
Joined: 4-November 05
From: North Wales
Member No.: 542



QUOTE (nprev @ Jul 19 2017, 06:07 PM) *
(and how slowly orbiting) MU69 really is given that it took observable time to occult an exceedingly small stellar disc.


Considering how slow its orbital motion is relative to Earth's I would expect the latter is the main factor determining the speed of the occultation. My congratulations too for the achievement. It exemplifies what humble groundwork can contribute to a major space odyssey.
Go to the top of the page
 
+Quote Post
abalone
post Jul 20 2017, 12:34 PM
Post #411


Member
***

Group: Members
Posts: 347
Joined: 12-June 05
From: Kiama, Australia
Member No.: 409



QUOTE (nprev @ Jul 20 2017, 03:07 AM) *
Amazing! The animated gif in the article clearly shows a gradual dimming and brightening...surely a demonstration of how small (and how slowly orbiting) MU69 really is given that it took observable time to occult an exceedingly small stellar disc.

Remarkable achievement, Alan, as per you & your team's usual. smile.gif

Great news, 5 occultations, so the obvious questions are why didn't any of the scopes detect it on 3rd June and what are the Sofia results?
Go to the top of the page
 
+Quote Post
Alan Stern
post Jul 20 2017, 01:13 PM
Post #412


Member
***

Group: Members
Posts: 493
Joined: 19-February 05
Member No.: 173



QUOTE (nprev @ Jul 19 2017, 06:07 PM) *
Amazing! The animated gif in the article clearly shows a gradual dimming and brightening...surely a demonstration of how small (and how slowly orbiting) MU69 really is given that it took observable time to occult an exceedingly small stellar disc.

Remarkable achievement, Alan, as per you & your team's usual. smile.gif


Thanks! But as I've said before, I'm just the symphony conductor here. In this case Marc Buie led the effort. He and his team just NAILED it!
Go to the top of the page
 
+Quote Post
Alan Stern
post Jul 20 2017, 01:14 PM
Post #413


Member
***

Group: Members
Posts: 493
Joined: 19-February 05
Member No.: 173



QUOTE (abalone @ Jul 20 2017, 01:34 PM) *
Great news, 5 occultations, so the obvious questions are why didn't any of the scopes detect it on 3rd June and what are the Sofia results?


June 3rd got the hazard search we wanted done but didn't put telescopes in the right place because back then we didn't have the MU69 orbit prediction well enough in hand. Subsequent HST June-July data helped with that.
Go to the top of the page
 
+Quote Post
JRehling
post Jul 20 2017, 05:06 PM
Post #414


Senior Member
****

Group: Members
Posts: 1968
Joined: 20-April 05
Member No.: 321



QUOTE (ngunn @ Jul 19 2017, 04:13 PM) *
Considering how slow its orbital motion is relative to Earth's I would expect the latter is the main factor determining the speed of the occultation.


That's definitely true. In fact, with both objects revolving the same way, it's more the Earth's motion minus the occulter's motion (near opposition) that determines the speed of the occultation. This is the reason why Venus and Mars have longer synodic periods than Neptune and Pluto.
Go to the top of the page
 
+Quote Post
jasedm
post Jul 20 2017, 08:34 PM
Post #415


Member
***

Group: Members
Posts: 602
Joined: 22-January 06
Member No.: 655



Phenomenal and diligent work ensuring the occultation was observed. Congratulations all.

Does anybody know if there are any plans to provide 2014 MU69 with a name prior to the flyby? (can't seem to find anything online)
Go to the top of the page
 
+Quote Post
Tom Tamlyn
post Jul 20 2017, 09:42 PM
Post #416


Member
***

Group: Members
Posts: 314
Joined: 1-July 05
From: New York City
Member No.: 424



From an April 28 blog post by Alan Stern:

QUOTE
One last thing I want to tell you is something I get asked a lot about. Yes, we’re going to give 2014 MU69 a real name, rather than just the “license plate” designator it has now. The details of how we’ll name it are still being worked out, but NASA announced a few weeks back that it will involve a public naming contest. Look for more information on that in the fall.


https://blogs.nasa.gov/pluto/2017/04/28/no-...-back-on-earth/

Edit: I didn't find this through a search on the naming issue; I just happened to look for the latest NH blog post the other day.

This post has been edited by Tom Tamlyn: Jul 20 2017, 10:10 PM
Go to the top of the page
 
+Quote Post
Tom Tamlyn
post Jul 20 2017, 10:08 PM
Post #417


Member
***

Group: Members
Posts: 314
Joined: 1-July 05
From: New York City
Member No.: 424



Earlier today Dr. Stern mentioned that the June 3 observations "got the hazard search we wanted done," even though no occultations were observed.

The interesting posts unthread from HSchirmer starting here helped me to understand how negative occultation results can provide some information about 2014 MU69's orbit and perhaps some constraints on its size that confirms previous calculations.

I'm puzzled how the team could glean information about hazards in the absence of an occultation, except perhaps by grossly negating the existence of extremely large companion objects, the existence of which would already seem unlikely.

I'm also curious about the SOFIA results. Has an occultation not yet been confirmed by analysis, or have the SOFIA results possibly been overtaken in importance by the multiple observations taken on July 17?
Go to the top of the page
 
+Quote Post
Hungry4info
post Jul 21 2017, 02:18 AM
Post #418


Senior Member
****

Group: Members
Posts: 1095
Joined: 26-July 08
Member No.: 4270



QUOTE (Tom Tamlyn)
I'm puzzled how the team could glean information about hazards in the absence of an occultation, except perhaps by grossly negating the existence of extremely large companion objects, the existence of which would already seem unlikely.

With occultations in hand, we have a much better idea of the orbit and position of 2014 MU69. The non-detection from the first observations can then be "re-calculated" to show that in a chord that passes near the asteroid, no debris was seen. For example here are numerous observations of a similar event for 90 Antiope. Several observations failed to detect anything, so each non-detection can allow you to place upper limits to the amount of dust in the area near the asteroid.

Edit: Perhaps a more illustrative example is Chariklo, where stellar occultations that missed the main body still allowed for the detection of rings around it.
Attached thumbnail(s)
Attached Image
 


--------------------
-- Hungry4info (Sirius_Alpha)
Go to the top of the page
 
+Quote Post
Tom Tamlyn
post Jul 21 2017, 06:21 AM
Post #419


Member
***

Group: Members
Posts: 314
Joined: 1-July 05
From: New York City
Member No.: 424



Thanks, that's very helpful.

I had assumed that the sixteen inch Dobsonians deployed by the team weren't powerful enough to detect the occultation of rings or satellites on their own, but rather that the existence of rings/satellites could only be inferred by the crispness of the edge of the main body's image. I didn't have any basis for that assumption, and I see from an arxiv paper on the Chariklo ring discovery occultation that ring-only observations were made by instruments with an aperture of approximately ten inches.

I also found this discussion on the NH website:

"
QUOTE
Combined, the pre-positioned mobile telescopes captured more than 100,000 images of the occultation star that can be used to assess the environment around this Kuiper Belt object (KBO). While MU69 itself eluded direct detection, the June 3 data provided valuable and unexpected insights that have already helped New Horizons.

These data show that MU69 might not be as dark or as large as some expected," said occultation team leader Marc Buie, a New Horizons science team member from Southwest Research Institute (SwRI) in Boulder, Colorado. * * *

Besides MU69's size, the readings offer details on other aspects of the Kuiper Belt object.

"These results are telling us something really interesting," said New Horizons Principal Investigator Alan Stern, of SwRI. "The fact that we accomplished the occultation observations from every planned observing site but didn't detect the object itself likely means that either MU69 is highly reflective and smaller than some expected, or it may be a binary or even a swarm of smaller bodies left from the time when the planets in our solar system formed."


http://pluto.jhuapl.edu/News-Center/News-A...p?page=20170706


Go to the top of the page
 
+Quote Post

28 Pages V  « < 26 27 28
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 28th July 2017 - 05:08 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.