Cabeus_A1 images from Gemini GMOS (2009-Sep-11-13:12UT) and suggested pointing sequence

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Dr. Diane Wooden

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Sep 12, 2009, 12:08:20 AM9/12/09
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Hello LCROSS astronomers:
Here is a GMOS image in .png and .jpg format for pointing, taken in
Gemini-N on 2009-Sep-11-13:12 UT. The exact slit positions will be
revised before impact after image analyses by Diane Wooden w.r.t.
coordinates supplied by the LCROSS Mission and the shadow models.

I am posting 3 images and an ejecta flux prediction (W/(m^2 um
arcsec^2)) versus Wavelength (um) for 3 different values of the grain
column density (1E7 m^-2 represents 4-20 sec; 2E5 m^-2 represents
30-90 sec). The brighter part of the ejecta plume reaches about 1.5
to 3 arc sec in height and spreads to 15"-30" wide in 120-240 sec.
The grain column densities are based on models by LCROSS Science Team
Member D. Goldstein (Goldstein, D.B. et al. 2008, Amer. Inst. Phys.
1084, 1061).

Gemini-N GMOS image from 2009-Sep-11-13:12UT in two formats, at G-band
(398-552 nm)+ RG610 (blue blocking) to avoid saturation. (http://
www.gemini.edu/sciops/instruments/gmos/imaging/filters/gmosn-filters)
mrgN20090911S0308.jpg
mrgN20090911S0308.png

Gemini-N Acquisition Camera image with pointing craters labeled.
cabeus_region_pointing_Cabeus_A1.pdf

Flux calculations based on number density of lofted 35um regolith
grains.
ejecta_flux_predict_09sep02.pdf

I have added labels to the Gemini Acquisition Camera image to show the
craters relevant for pointing to Cabeus A1.
When showing these images, please site:
2009-Sep-11-13:12UT GMOS Gemini-N (GN-2009B-Q-35)
LCROSS Ground-Based Observation Campaign, Mauna Kea Spectroscopy Team
D. Wooden, C. Woodward, P. Lucey, D. Harker, E. Young, M. S. Kelley,
T. Geballe, M. DiSanti, A. Conrad, D. Goldstein, A. Stephens, K. Roth,
J. Rayne

Suggested Pointing Sequence for Spectroscopy
Casatus_C_Waypt1
Newton_E_Waypt2
Waypt3
Cabeus_A1

Pointing coordinates refer to the observer's centroid on the
elliptical shape of the crater, not on the common designation
coordinates.

Pointing_Designation lon lat altitude
----------------- ------ ------- --------
Casatus_C_Waypt1 330.23 -72.195 0 km
Newton_E_Waypt2 323.79 -79.820 -1.3 km
Waypt3 321.22 -81.062 -1.0 km
Cabeus_A1 316.90 -81.55 -2.0 km Altitude
for Sun-Horizon

Bettinus 330.23 -72.195 0 km
Alternative to Casatus_C_Waypt1 as lunar phase wanes

In JPL horizons, derive Right Ascension and Declination and lunar
tracking rates by
using g: long, lat, altitude @301 in the OBJECT SEARCH BOX - see
attached screen grab as an example.



Cheers,
Dr. Diane Wooden
Astrophysicist
NASA Ames
LCROSS Mission Science Team Member
Co-PI of LCROSS Ground-Based Observation Campaign, Mauna Kea
Spectroscopy Team

PS To learn more, see the American Geophysical Union abstracts
click on Scientific Abstracts http://www.agu.org/meetings/fm09/program/index.php
and then in the next window,
Search for Author Wooden, D.H. and Abstract Title Key Word Search
LCROSS at

cano...@yahoo.com

unread,
Sep 12, 2009, 5:54:00 PM9/12/09
to LCROSS_Observation
Thanks for the update and paper references, Dr. Wooden. Amateur
astronomers, and a good part of the professional community, work in
apparent brightness units of integrated Johnson V magnitudes or
Johnson V magnitudes per square arcsec.

Can you provide us with translated values?

Thanks, Kurt
> click on Scientific Abstractshttp://www.agu.org/meetings/fm09/program/index.php

cano...@yahoo.com

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Sep 12, 2009, 6:10:29 PM9/12/09
to LCROSS_Observation
My apologies. I see that you already have the profile for a mag V
star plotted on file "ejecta_flux_predict_09sep02.pdf".

For amateur imaging purposes, it would be helpful to have your
conversion of 5 mag star in integrated magnitude to magnitudes per
square.

Is there a photometric reading for the shadowed region? For amateur
imaging purposes, it is helpful, if not necessary, to also know the
magnitudes per square arcsec of the shadowed portion of the target
crater. There needs to be a sufficient contrast between the shadow and
the plume for it to be imaged or seen visually.

Thanks, Kurt

On Sep 11, 10:08 pm, "Dr. Diane Wooden" <dwoo...@mac.com> wrote:
> click on Scientific Abstractshttp://www.agu.org/meetings/fm09/program/index.php

Jim Mosher

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Sep 13, 2009, 10:58:51 AM9/13/09
to LCROSS_Observation
Dear Dr. Wooden,

Thanks for sharing this information.

The following questions come to mind:

1. Could you be more explicit about the location of the dust cloud
reference "Goldstein, D.B. et al. 2008, Amer. Inst. Phys. 1084,
1061"? I am not familiar with a journal called "Amer. Inst. Phys.".
Is it available on-line?

2. Could you be more explicit about the time and location at which the
predicted column density of 1E7 m^-2 applies? I assume this is
referring to the expected density at the lowest height where sunlight
can be found over the target location? Does your statement that "the
brighter part of the ejecta plume reaches about 1.5 to 3 arc sec in
height" mean relative to the starting point on the crater floor or
relative to the point at which it reaches sunlit? Over how many
projected square arc-seconds horizontally and vertically is the
surface brightness shown in the red curve expected? Will this be seen
throughout the interval of 4-20 sec post impact, or only for some
portion of that interval? Finally, does "a = 35 micron" mean
particles of 35 micron radius or diameter?

3. Regarding the ~35x brighter curve for "a = 1 micron" particles
versus "a = 35 micron" particles at 30-90 sec, does this mean an
impact scenario with the ejected mass forming small particles is as
likely as one with it forming larger particles? Also, does it mean
the assumed particle size has no effect on the predicted size or shape
of the cloud other than in number density? And does it apply to the
red 4-20 sec curve as well (that is, would it, too, be 35x brighter at
visible wavelengths if the particles were "a = 1 micron" instead of "a
= 35 micron")?

4. How does the peak radiance of 9E-10 W m^-2 micron^-1 arcsec^-2
compare to the modeled radiance of the solid sunlit surface of the
Moon at "Cabeus_A1" as seen from Earth at the impact phase?

5. Could you be more explicit about how grain column densities were
converted to surface brightness? The fraction of the line of sight
filled by 1E7 particles m^-2 would be only 0.038 if 35 microns is a
diameter or 0.010 if it is a diameter. For visual observers, either
size is much larger than the wavelength of light, so I would assume
they can be regarded as opaque (Lambertian?) spheres lit at the same
phase angle as the Moon. How can such a small number of particles
produce such a high reflectance?

6. Could you be more explicit about how the crater coordinates were
determined? My understanding was that crater coordinates (at least
the longitude and latitude) have always referred to the centroid of
the of the rim (seen as an elliptical shape from Earth). By "common
designation coordinates" do you mean IAU catalog coordinates? Are
your coordinates for the centroid of "Cabeus_A1" based on the USGS
ULCN2005 warped Clementine and/or Lunar Orbiter products, on
independent Kaguya measurements, Earth-based radar maps, or some other
source?

7. The resolution and scale of the Gemini N image is not particularly
impressive by amateur standards. Is this a slit-jaw image of some
sort? What is the native scale in arc-sec per pixel? Is the resolution
of the present image limited by seeing, by focus errors, or was it
reduced in the reproduction? The scale of the images as posted is 0.84
arcsec/pixel and in Clavius the smallest craters detected seem to be
about 2.5-3 km in diameter -- about the same as skilled amateur can
achieve (in good seeing conditions) with a 50 mm aperture:

http://ltvt.wikispaces.com/Crater+Resolution

Does the Gemini-N GMOS spectrograph have a capability to use adaptive
optics to combat bad seeing? Any idea what the odds are of it
detecting kilometer-sized craters at a random moment (as at impact
time)?

Thanks,

Jim
> click on Scientific Abstractshttp://www.agu.org/meetings/fm09/program/index.php

cano...@yahoo.com

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Sep 13, 2009, 6:03:38 PM9/13/09
to LCROSS_Observation
On Sep 13, 8:58 am, Jim Mosher <jimmos...@gmail.com> wrote:
> 1. Could you be more explicit about the location of the dust cloud
> reference "Goldstein, D.B. et al. 2008, Amer. Inst. Phys. 1084,
> 1061"?  I am not familiar with a journal called "Amer. Inst. Phys.".
> Is it available on-line?

Goldstein, D. B.; Summy, D.; Colaprete, A.; Varghese, P. L.; Trafton,
L. M. 2008. Modeling the Vapor and Dust Dynamics Due to the Impact of
the LCROSS Spacecraft on the Moon. Proceedings of the 26th
International Symposium on Rarified Gas Dynamics. AIP Conference
Proceedings, Volume 1084, pp. 1061-1066 (2008).
http://adsabs.harvard.edu/abs/2008AIPC.1084.1061G

See also:

Summy, D.; Goldstein, D. B.; Colaprete, A.; Varghese, P. L.; Trafton,
L. M. 2009. LCROSS Impact: Dust and Gas Dynamics. 40th Lunar and
Planetary Science Conference, (Lunar and Planetary Science XL), held
March 23-27, 2009 in The Woodlands, Texas, id.2267.
http://adsabs.harvard.edu/abs/2009LPI....40.2267S
http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2267.pdf

- Kurt

Jim Mosher

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Sep 13, 2009, 11:31:14 PM9/13/09
to lcross_ob...@googlegroups.com
Thanks for the link, Kurt. I'll check it out next time I'm at a
library with a subscription.

- Jim

Jim Mosher

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Nov 7, 2009, 7:21:10 PM11/7/09
to LCROSS_Observation
I notice there is a brief description of the mysterious "Ejecta Flux
Predictions" diagram:


http://01227941410742638900-a-g.googlegroups.com/web/ejecta_flux_predict_09sep02.pdf?hl=en&gda=KXwUQFEAAACwPjh7SItssvxptLN2TxYMESz5CdghRDsqvL4v4jfXSsf6BnDYuLVmMAUWOblHGowMBYBYm1nev0Mv5LzGbk8iUwk_6Qi3BU8HCN0q6OYwM5VxXgp_nHWJXhfr7YhqVgA

in a paper ("SPECTROSCOPY OF THE LCROSS EJECTA PLUME FROM KECK,
GEMINI, AND NASA IRTF OBSERVATORIES ON MAUNA KEA") linked to from the
LEAG 2009 program page:

http://www.lpi.usra.edu/meetings/leag2009/pdf/2058.pdf

Since the text seems to be from an old paper (referring to the impact
in the future tense), rather than the content one would expect to see
at a November 16-19, 2009 meeting where preliminary LCROSS results are
supposed to be announced, I suspect the link may go bad, or a
different paper will be substituted for the present one, so I'll copy
the caption:

FIGURE: LCROSS Ejecta Plume Flux Predictions.

Flux density per square-arcsec (Total = Scattered + Thermal) for a
grain column density of 35 μmradius grains of N=1E7 m-2 and Ngr=2E5
m-2, representing post-impact intervals of 4 to 30 s and 60 to 90 s
(Goldstein model, [1] ), respectively. If a column density of Ngr=2E5
m-2 of 35 μm grains are disaggregated
to 1 μm grains, the flux density is much brighter (because a unit mass
of ejecta has greater surface area as smaller grains, and because
smaller grains have
higher albedos at near-IR wavelengths) and the shape of the spectrum
better reveals the composition. In the figure, if the mass-equivalent
of N=2E5 m-2 of 35 μm
radii grains disaggregate to N=1E10 m-2 of 1 μm grains, the flux
density is approximately the same as if the the case for N=1E7 m-2 of
35 μm grains except for
the discernment of mineral bands. Preliminary flux calculations use
pyroxene (Mg0.5,Fe0.5)SiO3 grains to mimic regolith composition.

References: [1] Goldstein D.B., et al. (2008) AIP, 1084, 1061.

-- Jim

On Sep 13, 2:03 pm, "canopu...@yahoo.com" <canopu...@yahoo.com> wrote:
> On Sep 13, 8:58 am, Jim Mosher <jimmos...@gmail.com> wrote:
>
> > 1. Could you be more explicit about the location of the dust cloud
> > reference "Goldstein, D.B. et al. 2008, Amer. Inst. Phys. 1084,
> > 1061"?  I am not familiar with a journal called "Amer. Inst. Phys.".
> > Is it available on-line?
>
> Goldstein, D. B.; Summy, D.; Colaprete, A.; Varghese, P. L.; Trafton,
> L. M.  2008. Modeling the Vapor and Dust Dynamics Due to the Impact of
> the LCROSS Spacecraft on the Moon.  Proceedings of the 26th
> International Symposium on Rarified Gas Dynamics. AIP Conference
> Proceedings, Volume 1084, pp. 1061-1066 (2008).http://adsabs.harvard.edu/abs/2008AIPC.1084.1061G

Jim Mosher

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Nov 9, 2009, 9:22:18 PM11/9/09
to LCROSS_Observation
Speaking of the "LCROSS Ejecta Flux Predictions" graph, those who
follow such things may recall that some of us have been struggling to
understand the varying photometric units used on the LCROSS charts.

The upper (red) line in this particular chart peaks at a spectral
radiance of about 9x10^-10 W m^-2 micron^-1 arc-sec^-2 in the visible,
which using the geometric equivalence of 1 arc-sec^-2 = 2.35x10^-11
steradians, can be expressed as 38 W m^-2 micron^-1 sr^-1 .

This was thought (at least by me) to be an extremely optimistic
estimate of the reflectance that might be produced by the stated
number of particles, and corresponds to about 4.0 visual magnitudes
per square-arc-sec (about the same as the surface brightness of Mars,
or of a solid piece of the Moon at this phase).

Possibly I am still misunderstanding the LCROSS team's use of
photometric units, or their method of integration, but the preliminary
light curve of the impact plume:

http://www.nasa.gov/394533main_VSP-NSP-total-radiance.png

shown on the Impact Images page:

http://www.nasa.gov/mission_pages/LCROSS/main/LCROSS_impact_images.html

appears to assign to the dark floor of Cabeus a radiance of 90-140 W
m^-2 sr^-1, with the plume, at its brightest, essentially doubling
that number to ~215 W m^-2 sr^-1. This value is said to be integrated
over the wavelength range of the UV-VIS instruments, suggesting the
peak spectral radiance (in per micron units) might be 1.5 to 2 times
higher than these numbers.

In view of the general perception of disappointment with the
brightness of the sunlit LCROSS plume, it seems surprising that the
reported numbers are actually much higher than what seemed an already
optimistic prediction.

On the face of things, the reported numbers would give the dark floor
of Cabeus a brightness on the order of 2.4 to 2.1 mpsas (roughly 4 to
6x the surface brightness of Mars [3.9 mpsas] and 1/3rd or 1/4th the
surface brightness the clouds of Venus [0.8 mpsas]), with the plume
developing to twice that brightness. Although the point where LCROSS
detected the plume (the point where the ejecta reached sunlight) may
have been hidden from Earth-based observers, at least part of the
shadowed floor of Cabeus can be seen. The reported brightness estimate
does not look correct.

As a second quick reality check on these numbers, from outside the
Earth's atmosphere the Sun has a wavelength-integrated surface
brightness (including IR as well as UV-VIS wavelengths) of about
2.0x10^7 W m^-2 sr^-1 (based on a solar constant of 1360 W m^-2
produced by an approximately uniform 6.8x10-5 sr source, or a
luminosity of 3.83x10^26 W from a Lambertian surface with a radius of
6.96x10^8 m). The Full Moon as seen from Earth has a similar spectrum
and is about 400,000x less bright than the Sun, so it should have a
wavelength-integrated surface brightness of ~50 W m^-2 sr^-1. By that
line of reasoning, the LCROSS graph seems to be reporting that the
dark floor of Cabeus was observed to be 2 to 3x as bright as piece of
the Full Moon as seen from Earth (which is significantly brighter than
a piece of the Moon at some other phase, or seen from some other
angle; and by inference must be about twice as bright as the surface
of Mars).

By either line of reasoning, 90-140 W m^-2 sr^-1 is an extraordinarily
high value for the brightness of the shadowed floor of Cabeus. It
will be interesting to see if these numbers for Cabeus and the plume
(or their units) change in future reports of the LCROSS observations.

-- Jim


On Nov 7, 4:21 pm, Jim Mosher <jimmos...@gmail.com> wrote:
> I notice there is a brief description of the mysterious "Ejecta Flux
> Predictions" diagram:
>
> http://01227941410742638900-a-g.googlegroups.com/web/ejecta_flux_pred...
> > March 23-27, 2009 in The Woodlands, Texas, id.2267.http://adsabs.harvard.edu/abs/2009LPI....40.2267Shttp://www.lpi.usra....
>
> > - Kurt
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