Overview

The Interstellar Medium Absorption Gradient Experiment Rocket (IMAGER) launched on Wednesday, November 21 at 3:55AM MST from White Sands, New Mexico. IMAGER probes the correlation between dust extinction, and the metallicity and radiation environment in M101 at ultraviolet wavelengths.

IMAGER simultaneously imaged the nearby spiral galaxy M101 in three 400Å wide bandpasses, measuring the apparent strength of the 2175Å bump and the UV continuum. With photometry from IMAGER and data from Spitzer, we will examine the morphology in the UV extinction curve and the IR emission features as a function of metallicity and radiation field hardness. This study will directly impact our understanding of the nature of dust and our ability to accurately account for the effects of dust on observations at all redshifts.

Science

Evidence from studies of starburst galaxies indicates that active formation of high mass stars modifies the UV dust extinction curve as seen by a lack of the characteristic 2175Å bump (Englebracht et al. 2008). The face-on spiral galaxy M101 is an ideal laboratory for the study of dust near regions of massive star formation, with many well studied HII regions and a steep metallicity gradient, log(O/H)+12 = 7.4→ 8.8 (Kennicutt et al. 2003).

What is the origin of the 2175Å extinction bump? Some dust grain models suggest that the 2175Å bump and the aromatic features (seen in Spitzer data) are carried by the same material (Li & Draine 2002). Spitzer Space Telescope observations have revealed that the strength of the aromatic features (PAH features) correlates better with radiation field hardness than with metallicity. This suggests that the small grains are being processed from radiation in these HII regions. We examine if this correlation extends to the UV- are the UV extinction features best correlated with the aromatic features and radiation hardness, or are they better correlated with the metallicity?

To detect the strength of the ultraviolet extinction features and the continuum, IMAGER capitalizes on three uniquely defined bandpasses, which will provide an excellent probe of this hypothesis that the 2175Å bump and the aromatic features are carried by the same material.

Instrument

Mechanical layout and combined with Zemax raytrace of the IMAGER instrument.

Photos from assembly of the IMAGER telescope. Far left: Secondary mirror mount with accordion and clamp reed structure. Left: Primary and Secondary mounted within the telescope tube. Right: Primary whiffle-tree mirror mount. Far Right: Off axis tertiary mirror in hexapod mount.

Telescope f/12.29 Ritchey-Chretien; AlMgF2, coated for high reflectance in the UV at NASA GSFC
Primary and Secondary 0.5 meter, primary mounted with whiffle tree design ; .12 meter convex secondary, mounted with spring and stainless steel accordion design , with clamping reeds, optimized for alignment ; set polished at Optical Mechanics, Inc.
Tertiary Mirror .1 meter off axis parabolic mirror from SORL mounted with hexapod structure
Field of View 30 arcminutes, fits M101 with pointing and alignment tolerances
Camera Assembly Anodized assembly containing four custom beamsplitting dichroics from Acton Optics, 11 lenses in MgF2, and CaF (9 COTS), and 9 COTS AlMgF, fold mirrors from CVI Melles Griot and Edmund Optics
Readout Electronics Refurbished previously flown sounding rocket electronics to read wedge-and-strip anodes
Detector 40mm microchannel plate detector from Photek Ltd., with CsTe photocathode on a MgF2 window for high QE in UV. microchannel pores are 3x10μm, 107 gain, in resistive sea configuration with 4 wedge and strip anodes at detector focal plane, each anode with a square active area of 400mm2.

Launch

IMAGER launched at 3:55 MST from White Sands Missile Range in New Mexico. It reached an apogee of 293km (182 miles) and collected data in the UV for 380seconds. 15 minutes after launch, it landed ~50 miles downrange. The IMAGER experiment crew joined NSROC team members and WSMR personnel for a flight on a Huey helicopter to retrieve the payload.

Launch video-composite video of range cam, 30ft cam, and camera located in the IMAGER control room.
 
 


 
 
 
 


Results

We have collected 380s of on-target data in 3 ultraviolet bands. We combine this data with knowledge of detector and instrument distortions, as well as lab-based wavelength calibration to produce reduced science data.

To examine the strength of the 2175Å feature, we will perform aperture photometry on the HII regions in M101. Then, we will generate color-color plots and compare to theoretical curves based on models of stellar evolution and radiative transfer effects. We compare the strength of this feature at a given galactic location to the local galactic properties (radiation field hardness and metallicity). If the 2175Å feature traces the aromatic features, we would expect the central region to have the same bump strength, declining past a central 'threshold radius'.

Team

WSMR IMAGER Team with the assembled rocket.

WFF IMAGER Team with the payload on the shake table.

IMAGER SCIENCE TEAM:

Principal Investigator: Professor Timothy Cook, UML

Project Scientist: Meredith Danowski, Boston University

Project Scientist: Dr. Karl Gordon, Space Telescope Science Institute

Project Engineer: Dr. Brian Hicks, UML

Mechanical Engineer: Jason Martel, UML

Project Scientist: Chris Mendillo, Boston University

Project Scientist: Ewan Douglas, Boston University

Co-Investigator: Professor Supriya Chakrabarti, UML

Press

UML post-doc Dr. Brian Hicks works during intergration at the Wallops Flight facility to install Shutter Door cables.

UML News, December 7, 2012: Physics Professor Rocket Launch a Success; Instrument Observed Distant Spiral Galaxy M101 (http://www.uml.edu/News/stories/2011-12/Rocket-launch.aspx)

NASA Mission update, November 21, 2012: IMAGER Launch Successful (http://www.nasa.gov/mission_pages/sounding-rockets/news/imager-dd.html)

Sounding Rocket, Fourth Quarter 2012 Report: 36.260 UG Cook- IMAGER successfully launched November 21, 2012 (http://sites.wff.nasa.gov/code810/files/Rocket_Report_4th_qt_2012.pdf)

UML News, October 25, 2012: Astrophysicist Set to Launch Rocket Experiment; Instrument Will Observe Spiral Galaxy Near Big Dipper's Handle (http://www.uml.edu/News/stories/2011-12/Cook-rocket-experiment.aspx)

Sounding Rocket, Third Quarter 2012 Report: Integration and Testing 36.260 UG Cook- IMAGER (http://sites.wff.nasa.gov/code810/files/Rocket_Report_3rd_qt_2012.pdf)

BU grad student Meredith Danowski installs cables and connectors on the payload assembly.

NSROC ACS Engineer Nate Empson and UML Mechanical Engineer Jason Martel prepare for alignment tests at WFF.

IMAGER team watches the installation of the payload on the spin table at WFF. L-R Dr. Brian Hicks, Christian Ward, Jason Martel, Frank Ward, Meredith Danowski

IMAGER crew prepares for horizontal tests at WSMR.
 
 

Outreach

COMING SOON
Public talks and presentations from IMAGER team members and links to inquiry based curricula about rockets and space!

Acknowledgements - webdesign: Mooshe Nickerson - Comments/questions? E-mail: Meredith Danowski