Spitzer Liquid He Options

[deglr6328]

How much cryogen does Spitzer have remaining in its dewar? Do they know, or are they just waiting to see a temperature rise after complete boil-off? Can't find much info on the website.

[DEChengst]

Don't know about the current estimate, but during launch the helium was estimated to last until 2008 or 2009.

[deglr6328]

wow, weird that GP-B's only lasted a single year an had like 8 times the total volume.

[djellison]

But GP-B had to be kept a lot lot colder than Spitzer does.

Doug

[deglr6328]

mmmnah same temp I think. Superfluid He at ~1.5K. Right? Perhaps the cold volume in Spitzer is just less massive than GP-B's "science package". Or maybe GP-B just has to deal with more thermal radiation from Earth since it's in LEO. In fact, yes, now that I think about it I'd be willing to bet this is the reason the He ran out so much faster on GP-B.

[djellison]

Nope - you're right - same temp. - for some reason I thought Spitzer was kept a bit warmer than GPB

The LEO issue is almsot certainly a clincher though -

[tfisher]

Or maybe GP-B just has to deal with more thermal radiation from Earth since it's in LEO. In fact, yes, now that I think about it I'd be willing to bet this is the reason the He ran out so much faster on GP-B.

You nailed that one on the head. Here's what this page about Spitzer's orbit has to say:

Spitzer will drift away from Earth at the rate of ~ 0.1 AU/year. [An AU, or Astronomical Unit, is the average distance between the Sun and Earth, or about 150 million kilometers]. Since the Observatory must be cooled to within a few degrees of absolute zero, this orbit choice offers a more benign thermal environment than any geocentric orbit. Earth not only reflects visible light from the Sun, but it also emits warm infrared radiation. Any satellite in a reasonable geocentric orbit would therefore be bathed in temperatures exceeding 250 Kelvin (K). The drifting heliocentric orbit places Spitzer in "deep space," where the ambient temperatures are about 30 to 40 K. By using Nature to assist in cooling the Observatory, Spitzer can carry much less liquid helium cryogen than it would need in an Earth orbit.

[hendric]

Will Spitzer be useful once the Helium runs out?

[Circum]

Keep in mind that some of GPB's helium was used to spin up the gyros and also for the micro-thrusters, although I admit I'm not sure of the volumes used for those purposes relative to cooling.

[deglr6328]

Will Spitzer be useful once the Helium runs out?

That's an interesting thought. If it ends up equilibrating at 30-40K after He boiloff I could imagine it still getting some useful data from the shorter wavelength IRAC sensors at ~3-5 microns. I should think that the noise wouldn't be too high to prevent some imaging in that band. hmmm. But then this is barely above the range of the Hubble NICMOS and you'd have the question of whether or not it would be economically worth it. (well, assuming that Hubble is still operating of course)

What I don't get is if it has such an incredibly low boiloff rate to begin with (something like a few milliliters per hour) why wouldn't they look at attaching something like this to reliquefy some of the helium? I would think that even with a modest investment in power from larger solar arrays (say.... 1 KW) you could easily double the mission lifetime by reducing the boiloff rate, if not eliminating it completely.

[ljk4-1]

Spitzer Space Telescope article in December, 2005 issue of National Geographic Magazine.

There's a lot hiding in the universe's dark corners. Interstellar dust clouds and inky stretches of deep space can appear dull to ordinary telescopes. But to a car-size telescope 26 million miles (42 million kilometers) from Earth, they are alive with light—infrared light, or heat rays. Since its launch in August 2003, says Robert Kennicutt, an astronomer at the University of Arizona, NASA's Spitzer Space Telescope "has opened up half the universe to us."

In the process, it has exposed cosmic birthplaces. Stars take shape in clouds of gas and dust, and planets emerge in disks of debris around new stars. Early galaxies are also swathed in dust. Little visible light gets out, but these objects still emit heat—and infrared.

http://www7.nationalgeographic.com/ngm/051...ure5/index.html

[ljk4-1]

Astrophysics, abstract
astro-ph/0511358

From: William T. Reach [view email]

Date (v1): Fri, 11 Nov 2005 16:32:59 GMT (59kb)
Date (revised v2): Thu, 17 Nov 2005 07:43:56 GMT (0kb,I)
Date (revised v3): Thu, 17 Nov 2005 21:57:35 GMT (0kb,I)
Date (revised v4): Fri, 13 Jan 2006 18:04:39 GMT (59kb)

The Dust cloud around the White Dwarf G 29-38

Authors: William T. Reach, Marc J. Kuchner, Ted von Hippel, Adam Burrows, Fergal Mullally, Mukremin Kilic, D. E. Winget

Comments: accepted for publication in the Astrophysical Journal Letters

Journal-ref: 2005, Astrophysical Journal Letters, volume 635, page L161

We present new observations of the white dwarf G 29-38 with the camera (4.5 and 8 microns), photometer (24 microns), and spectrograph (5.5-14 microns) of the Spitzer Space Telescope. This star has an exceptionally large infrared excess amounting to 3% of the bolometric luminosity. The spectral energy distribution has a continuum peak around 4.5 micros and a 9-11 micron emission feature 1.25 times brighter than the continuum. A mixture of amorphous olivine and a small amount of forsterite in an emitting region 1-5 Rsun from the star can reproduce the shape of the 9-11 micron feature. The spectral energy distribution also appears to require amorphous carbon to explain the hot continuum. Our new measurements support the idea that a relatively recent disruption of a comet or asteroid created the cloud.

http://arxiv.org/abs/astro-ph/0511358

[ljk4-1]

Astrophysics, abstract
astro-ph/0601495

From: Patrice Bouchet J.. [view email]

Date: Mon, 23 Jan 2006 01:45:09 GMT (761kb)

SN 1987A After 18 Years: Mid-Infrared GEMINI and SPITZER Observations of the Remnant

Authors: Patrice Bouchet, Eli Dwek, I. John Danziger, Richard G. Arendt, I. James M. De Buizer, Sangwook Park, Nicholas B. Suntzeff, Robert P. Kirshner, Peter Challis

Comments: 23 pages; 3 tables; 12 figures (Fig.2, Fig.4, and Fig.7 missing because too big; Fig.14 is provisory); submitted to ApJ January 2006

We present high resolution 11.7 and 18.3um mid-IR images of SN 1987A obtained on day 6526 with T-ReCS attached to the Gemini telescope. The 11.7um flux has increased significantly since our last observations on day 6067. The images clearly show that all the emission arises from the equatorial ring (ER). Spectra obtained with Spitzer, on day 6184 with MIPS at 24um, on day 6130 with IRAC in the 3.6-8um region, and on day 6190 with IRS in the 12-37um region show that the emission consists of thermal emission from silicate dust that condensed out in the red giant wind of the progenitor star. The dust temperature is ~166K, and the emitting dust mass is ~2.6 x 10-6 Msun. Lines of [Ne II]12.82um and [Ne III]15.56um are clearly present, as well as a weak [Si II]34.8um line. We also detect two lines near 26um which we tentatively ascribe to [Fe II]25.99um and [O IV]25.91um. Comparison of the Gemini 11.7um image with X-ray images from Chandra, UV-optical images from HST, and radio synchrotron images obtained by the ATCA show generally good correlation of the images across all wavelengths. Because of the limited resolution of the mid-IR images we cannot uniquely determine the location or heating mechanism of the dust giving rise to the emission. The dust could be collisionally heated by the X-ray emitting plasma, providing a unique diagnostic of plasma conditions. Alternatively, the dust could be radiatively heated in the dense UV-optical knots that are overrun by the advancing supernova blast wave. In either case the dust-to-gas mass ratio in the circumstellar medium around the supernova is significantly lower than that in the general ISM of the LMC, suggesting either a low condensation efficiency in the wind of the progenitor star, or the efficient destruction of the dust by the SN blast wave.

http://arxiv.org/abs/astro-ph/0601495

[ljk4-1]

Paper: astro-ph/0601633

Date: Fri, 27 Jan 2006 02:44:00 GMT (226kb)

Title: Spectacular Spitzer images of the Trifid Nebula: Protostars in a young,
massive-star-forming region

Authors: J. Rho, W. T. Reach (Spitzer Science Center/CalTech), B. Lefloch
(Laboratoire d'Astrophysique, Observatoire de Grenoble) and G. Fazio
(Harvard-Smithsonian Center for Astrophysics)

Comments: Accepted for publication in ApJ. Full resolution images are available
at http://spider.ipac.caltech.edu/staff/rho/
\\

Spitzer IRAC and MIPS images of the Trifid Nebula (M20) reveal its
spectacular appearance in infrared light, highlighting the nebula's special
evolutionary stage. The images feature recently-formed massive protostars and
numerous young stellar objects, and a single O star that illuminates the
surrounding molecular cloud from which it formed, and unveil large-scale,
filamentary dark clouds. The hot dust grains show contrasting infrared colors
in shells, arcs, bow-shocks and dark cores. Multiple protostars are detected in
the infrared, within the cold dust cores of TC3 and TC4, which were previously
defined as Class 0. The cold dust continuum cores of TC1 and TC2 contain only
one protostar each. The Spitzer color-color diagram allowed us to identify ~160
young stellar objects and classify them into different evolutionary stages. The
diagram also revealed a unique group of YSOs which are bright at 24 micron but
have the spectral energy distribution peaking at 5-8 micron. Despite
expectation that Class 0 sources would be "starless" cores, the Spitzer images,
with unprecedented sensitivity, uncover mid-infrared emission from these Class
0 protostars. The mid-infrared detections of Class 0 protostars show that the
emission escapes the dense, cold envelope of young protostars. The mid-infrared
emission of the protostars can be fit by two temperatures of 150 and 400 K; the
hot core region is probably optically thin in the mid-infrared regime, and the
size of hot core is much smaller than that of the cold envelope. The presence
of multiple protostars within the cold cores of Class 0 objects implies that
clustering occurs at this early stage of star formation. The TC3 cluster shows
that the most massive star is located at the center of the cluster and at the
bottom of the gravitational-potential well.

\\ ( http://arXiv.org/abs/astro-ph/0601633 , 226kb)

[ljk4-1]

News Release: 2006-019

February 8, 2006

NASA's Spitzer Uncovers Hints of Mega Solar Systems

NASA's Spitzer Space Telescope has identified two huge "hypergiant" stars circled by monstrous disks of what might be planet-forming dust. The findings surprised astronomers because stars as big as these were thought to be inhospitable to planets.

"These extremely massive stars are tremendously hot and bright and have very strong winds, making the job of building planets difficult," said Joel Kastner of the Rochester Institute of Technology in New York. "Our data suggest that the planet-forming process may be hardier than previously believed, occurring around even the most massive stars that nature produces."

Kastner is first author of a paper describing the research in the Feb. 10 issue of Astrophysical Journal Letters.

Dusty disks around stars are thought to be signposts for present or future planetary systems. Our own sun is orbited by a thin disk of planetary debris, called the Kuiper Belt, which includes dust, comets and larger bodies similar to Pluto.

Last year, astronomers using Spitzer reported finding a dust disk around a miniature star, or brown dwarf, with only eight one-thousandths the mass of the sun (http://www.spitzer.caltech.edu/Media/happenings/20051129/). Disks have also been spotted before around stars five times more massive than the sun.

The new Spitzer results expand the range of stars that sport disks to include the "extra large." The infrared telescope detected enormous amounts of dust around two positively plump stars, R 66 and R 126, located in the Milky Way's nearest neighbor galaxy, the Large Magellanic Cloud. Called hypergiants, these blazing hot stars are aging descendents of the most massive class of stars, referred to as "O" stars. They are 30 and 70 times the mass of the sun, respectively. If a hypergiant were located at the sun's position in our solar system, all the inner planets, including Earth, would fit comfortably within its circumference.

Astronomers estimate that the stars' disks are also bloated, spreading all the way out to an orbit about 60 times more distant than Pluto's around the sun. The disks are probably loaded with about ten times as much mass as is contained in the Kuiper Belt. Kastner and his colleagues say these dusty structures might represent the first or last steps of the planet-forming process. If the latter, then the disks can be thought of as enlarged versions of our Kuiper Belt.

"These disks may be well-populated with comets and other larger bodies called planetesimals," said Kastner. "They might be thought of as Kuiper Belts on steroids."

Spitzer detected the disks during a survey of 60 bright stars thought to be wrapped in spherical cocoons of dust. According to Kastner, R 66 and R 126 "stuck out like sore thumbs" because their light signatures, or spectra, indicated the presence of flattened disks. He and his team believe these disks whirl around the hypergiant stars, but they say it is possible the giant disks orbit unseen, slightly smaller companion stars.

A close inspection of the dust making up the disks revealed the presence of sand-like planetary building blocks called silicates. In addition, the disk around R 66 showed signs of dust clumping in the form of silicate crystals and larger dust grains. Such clumping can be a significant step in the construction of planets.

Stars as massive as R 66 and R 126 don't live very long. They burn through all of their nuclear fuel in only a few million years, and go out with a bang, in fiery explosions called supernovae. Their short life spans don't leave much time for planets, or life, to evolve. Any planets that might crop up would probably be destroyed when the stars blast apart.

"We do not know if planets like those in our solar system are able to form in the highly energetic, dynamic environment of these massive stars, but if they could, their existence would be a short and exciting one," said Charles Beichman, an astronomer at NASA's Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena.

Other authors of this work include Catherine L. Buchanan of the Rochester Institute of Technology, and B. Sargent and W. J. Forrest of the University of Rochester, N.Y.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. JPL is a division of Caltech. Spitzer's infrared spectrograph, which made the new observations, was built by Cornell University, Ithaca, N.Y. Its development was led by Jim Houck of Cornell.

An artist concept of a hypergiant and its disk, plus additional graphics and information, are available at http://www.spitzer.caltech.edu/spitzer . For more information about NASA and agency programs on the Web, visit

http://www.nasa.gov/home/ .