HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science

 

DAILY REPORT #5187

 

PERIOD COVERED: 5am September 22 - 5am September 23, 2010 (DOY 265/09:00z-266/09:00z)

 

FLIGHT OPERATIONS SUMMARY:

 

Significant Spacecraft Anomalies: (The following are preliminary reports

of potential non-nominal performance that will be investigated.)

 

HSTARS: (None)

 

COMPLETED OPS REQUEST: (None)

 

COMPLETED OPS NOTES: (None)

 

                       SCHEDULED      SUCCESSFUL

FGS GSAcq                  5               5                

FGS REAcq                   8               8                

OBAD with Maneuver    7               7                

 

SIGNIFICANT EVENTS: (None)

 

 

OBSERVATIONS SCHEDULED:

 

ACS/WFC 11996

 

CCD Daily Monitor (Part 3)

 

This program comprises basic tests for measuring the read noise and dark

current of the ACS WFC and for tracking the growth of hot pixels. The

recorded frames are used to create bias and dark reference images for

science data reduction and calibration. This program will be executed

four days per week (Mon, Wed, Fri, Sun) for the duration of Cycle 17. To

facilitate scheduling, this program is split into three proposals. This

proposal covers 308 orbits (19.25 weeks) from 21 June 2010 to 1 November

2010.

 

COS/NUV/FUV 11598

 

How Galaxies Acquire their Gas: A Map of Multiphase Accretion and

Feedback in Gaseous Galaxy Halos

 

We propose to address two of the biggest open questions in galaxy

formation - how galaxies acquire their gas and how they return it to the

IGM - with a concentrated COS survey of diffuse multiphase gas in the

halos of SDSS galaxies at z = 0.15 - 0.35. Our chief science goal is to

establish a basic set of observational facts about the physical state,

metallicity, and kinematics of halo gas, including the sky covering

fraction of hot and cold material, the metallicity of infall and

outflow, and correlations with galaxy stellar mass, type, and color -

all as a function of impact parameter from 10 - 150 kpc. Theory suggests

that the bimodality of galaxy colors, the shape of the luminosity

function, and the mass-metallicity relation are all influenced at a

fundamental level by accretion and feedback, yet these gas processes are

poorly understood and cannot be predicted robustly from first

principles. We lack even a basic observational assessment of the

multiphase gaseous content of galaxy halos on 100 kpc scales, and we do

not know how these processes vary with galaxy properties. This ignorance

is presently one of the key impediments to understanding galaxy

formation in general. We propose to use the high-resolution gratings

G130M and G160M on the Cosmic Origins Spectrograph to obtain sensitive

column density measurements of a comprehensive suite of multiphase ions

in the spectra of 43 z < 1 QSOs lying behind 43 galaxies selected from

the Sloan Digital Sky Survey. In aggregate, these sightlines will

constitute a statistically sound map of the physical state and

metallicity of gaseous halos, and subsets of the data with cuts on

galaxy mass, color, and SFR will seek out predicted variations of gas

properties with galaxy properties. Our interpretation of these data will

be aided by state-of-the-art hydrodynamic simulations of accretion and

feedback, in turn providing information to refine and test such models.

We will also use Keck, MMT, and Magellan (as needed) to obtain optical

spectra of the QSOs to measure cold gas with Mg II, and optical spectra

of the galaxies to measure SFRs and to look for outflows. In addition to

our other science goals, these observations will help place the Milky

Way's population of multiphase, accreting High Velocity Clouds (HVCs)

into a global context by identifying analogous structures around other

galaxies. Our program is designed to make optimal use of the unique

capabilities of COS to address our science goals and also generate a

rich dataset of other absorption-line systems.

 

COS/NUV/FUV/STIS/CCD/MA1 11692

 

The LMC as a QSO Absorption Line System

 

We propose to obtain high resolution, high signal-to-noise observations

of QSOs behind the Large Magellanic Clouds. These QSOs are situated

beyond the star forming disk of the galaxy, giving us the opportunity to

study the distribution of metals and energy in regions lacking

significant star formation. In particular, we will derive the

metallicities and study the ionization characteristics of LMC gas at

impact parameters 3-17 kpc. We will compare our results with high-z QSO

absorption line systems.

 

FGS 12320

 

The Ages of Globular Clusters and the Population II Distance Scale

 

Globular clusters are the oldest objects in the universe whose age can

be accurately determined. The dominant error in globular cluster age

determinations is the uncertain Population II distance scale. We propose

to use FGS 1r to obtain parallaxes with an accuracy of 0.2

milliarcsecond for 9 main sequence stars with [Fe/H] < -1.5. This will

determine the absolute magnitude of these stars with accuracies of 0.04

to 0.06mag. This data will be used to determine the distance to 24

metal-poor globular clusters using main sequence fitting. These

distances (with errors of 0.05 mag) will be used to determine the ages

of globular clusters using the luminosity of the subgiant branch as an

age indicator. This will yield absolute ages with an accuracy 5%, about

a factor of two improvement over current estimates. Coupled with

existing parallaxes for more metal-rich stars, we will be able to

accurately determine the age for globular clusters over a wide range of

metallicities in order to study the early formation history of the Milky

Way and provide an independent estimate of the age of the universe.

 

The Hipparcos database contains only 1 star with [Fe/H] < -1.4 and an

absolute magnitude error less than 0.18 mag which is suitable for use in

main sequence fitting. Previous attempts at main sequence fitting to

metal-poor globular clusters have had to rely on theoretical

calibrations of the color of the main sequence. Our HST parallax program

will remove this source of possible systematic error and yield distances

to metal-poor globular clusters which are significantly more accurate

than possible with the current parallax data. The HST parallax data will

have errors which are 10 times smaller than the current parallax data.

Using the HST parallaxes, we will obtain main sequence fitting distances

to 11 globular clusters which contain over 500 RR Lyrae stars. This will

allow us to calibrate the absolute magnitude of RR Lyrae stars, a

commonly used Population II distance indicator.

 

STIS/CCD 11845

 

CCD Dark Monitor Part 2

 

Monitor the darks for the STIS CCD.

 

STIS/CCD 11847

 

CCD Bias Monitor-Part 2

 

Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1,

and 1x1 at gain = 4, to build up high-S/N superbiases and track the

evolution of hot columns.

 

WFC3/UV 11605

 

Obtaining the Missing Links in the Test of Very Low Mass Evolutionary

Models with HST

 

We are proposing for spatially resolved ACS+HRC observations of 11 very

low mass binaries spanning late-M, L and T spectral types in order to

obtain precise effective temperature measurements for each component.

All of our targets are part of a program in which we are measuring

dynamical masses of very low-mass binaries to an unprecedented precision

of 10% (or better). However, without precise temperature measurements,

the full scientific value of these mass measurements cannot be realized.

Together, mass and temperature measurements will allow us to distinguish

between brown dwarf evolutionary models that make different assumptions

about the interior and atmospheric structure of these ultra-cool

objects. While dynamical masses can be obtained from the ground in the

near-IR, obtaining precise temperatures require access to optical data

which, for these sub-arcsecond binaries, can only be obtained from space

with Hubble.

 

WFC3/UV 12245

 

Orbital Evolution and Stability of the Inner Uranian Moons

 

Nine densely-packed inner moons of Uranus show signs of chaos and

orbital instability over a variety of time scales. Many moons show

measureable orbital changes within a decade or less. Long-term

integrations predict that some moons could collide in less than one

million years. One faint ring embedded in the system may, in fact, be

the debris left behind from an earlier such collision. Meanwhile, the

nearby moon Mab falls well outside the influence of the others but

nevertheless shows rapid, as yet unexplained, changes in its orbit. It

is embedded within a dust ring that also shows surprising variability. A

highly optimized series of observations with WFC3 over the next three

cycles will address some of the fundamental open questions about this

dynamically active system: Do the orbits truly show evidence of chaos?

If so, over what time scales? What can we say about the masses of the

moons involved? What is the nature of the variations in Mab's orbit? Is

Mab's motion predictable or random? Astrometry will enable us to derive

the orbital elements of these moons with 10-km precision. This will be

sufficient to study the year-by-year changes and, combined with other

data from 2003-2007, the decadal evolution of the orbits. The pairing of

precise astrometry with numerical integrations will enable us to derive

new dynamical constraints on the masses of these moons. Mass is the

fundamental unknown quantity currently limiting our ability to reproduce

the interactions within this system. This program will also capitalize

upon our best opportunity for nearly 40 years to study the unexplained

variations in Uranus's faint outer rings.

 

WFC3/UVIS 11905

 

WFC3 UVIS CCD Daily Monitor

 

The behavior of the WFC3 UVIS CCD will be monitored daily with a set of

full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K

subarray biases are acquired at less frequent intervals throughout the

cycle to support subarray science observations. The internals from this

proposal, along with those from the anneal procedure (Proposal 11909),

will be used to generate the necessary superbias and superdark reference

files for the calibration pipeline (CDBS).

 

WFC3/UVIS 11908

 

Cycle 17: UVIS Bowtie Monitor

 

Ground testing revealed an intermittent hysteresis type effect in the

UVIS detector (both CCDs) at the level of ~1%, lasting hours to days.

Initially found via an unexpected bowtie- shaped feature in flatfield

ratios, subsequent lab tests on similar e2v devices have since shown

that it is also present as simply an overall offset across the entire

CCD, i.e., a QE offset without any discernable pattern. These lab tests

have further revealed that overexposing the detector to count levels

several times full well fills the traps and effectively neutralizes the

bowtie. Each visit in this proposal acquires a set of three 3x3 binned

internal flatfields: the first unsaturated image will be used to detect

any bowtie, the second, highly exposed image will neutralize the bowtie

if it is present, and the final image will allow for verification that

the bowtie is gone.

 

WFC3/UVIS 11914

 

UVIS Earth Flats

 

This program is an experimental path finder for Cycle 18 calibration.

Visible-wavelength flat fields will be obtained by observing the dark

side of the Earth during periods of full moon illumination. The

observations will consist of full-frame streaked WFC3 UVIS imagery: per

22- min total exposure time in a single "dark-sky" orbit, we anticipate

collecting 7000 e/pix in F606W or 4500 e/pix in F814W. To achieve

Poisson S/N > 100 per pixel, we require at least 2 orbits of F606W and 3

orbits of F814W.

 

For UVIS narrowband filters, exposures of 1 sec typically do not

saturate on the sunlit Earth, so we will take sunlit Earth flats for

three of the more-commonly used narrowband filters in Cycle 17 plus the

also-popular long-wavelength quad filters, for which we get four filters

at once.

 

Why not use the Sunlit Earth for the wideband visible-light filters? It

is too bright in the visible for WFC3 UVIS minimum exposure time of 0.5

sec. Similarly, for NICMOS the sunlit-Earth is too bright which

saturates the detector too quickly and/or induces abnormal behaviors

such as super-shading (Gilmore 1998, NIC 098-011). In the narrowband

visible and broadband near- UV its not too bright (predictions in Cox et

al. 1987 "Standard Astronomical Sources for HST: 6. Spatially Flat

Fields." and observations in ACS Program 10050).

 

Other possibilities? Cox et al.'s Section II.D addresses many other

possible sources for flat fields, rejecting them for a variety of

reasons. A remaining possibility would be the totally eclipsed moon.

Such eclipses provide approximately 2 hours (1 HST orbit) of opportunity

per year, so they are too rare to be generically useful. An advantage of

the moon over the Earth is that the moon subtends less than 0.25 square

degree, whereas the Earth subtends a steradian or more, so scattered

light and light potentially leaking around the shutter presents

additional problems for the Earth. Also, we're unsure if HST can point

180 deg from the Sun.

 

 

 

-Lynn                                                  

Lynn F. Bassford               office#: 301-286-2876  
Hubble Space Telescope
CHAMP Mission Operations Manager
CHAMP Flight Operations Team Manager
Lockheed Martin Mission Services (LMMS)


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