Sarah StoebnerUniversity of Hawai’i at Hilo

Mentor: Billie Chitwood

Temperature Effects on the Pointing of Antennas at the Submillimeter Array

Outline

SMA

Why?

Background

Project

Results

The Submillimeter ArrayMauna Kea, Hawai’i

Important Project

-Daytime observations-Most temperature variation

-Metal heats up it expands

-Variation of expansion affects pointing

-Pointing important for astronomical data

-Other factors cause pointing errors-Correct for factors that cause large error

-Pointing Model-Too expensive to correct for all

Quadrapods

Primary Reflector

Sensor

Reflector Mount

Temperature Dataon July 25, 2007

Snapshotson July 25, 2007

Snapshot of Jupiter at sunset (7:32PM)

Snapshot of Jupiter a few hours later (10:13PM)

Jupiter Arcturus Vega Altair Deneb

ResultsIn Azimuth:

The pixel difference was 1.6 pixelsWith 1.252” per pixel the pointing error caused by temperature was 1.878”

In Elevation:

The pixel difference was 3.5 pixelsWith 1.252” per pixel the pointing error caused by temperature was 4.381”

Acknowledgments Billie Chitwood

Nimesh Patel

Erin Brassfield

SMA Staff

Sarah Anderson

Scott Seagroves

Hilary O’Bryan

This work has been supported by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement No. AST - 9876783.

Other Pointing Errors

Azimuth Error

Elevation Error

ΔEl = El´ + S cos(El) + I cos(Az) + I sin(Az) + I cos(2(Az)) + I sin(2(Az))

+ Qel

ΔAz cos(El) = Az´ cos(El) + C + L sin (El) + I sin(El) sin(Az) + I sin(El) cos(Az)

+ I sin(El) sin(2(Az)) + I sin(El) cos(2(Az)) + M cos(El) sin(Az) + M cos(El) cos(Az)

+ M cos(El) sin(2(Az)) + M cos(El) cos(2(Az)) + M cos(El) sin(3(Az))

+ M cos(El) cos(3(Az)) + Qaz +RMaz