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Adventures in Ground-based Astronomy: An Inside View (Part II)

August 24, 2012

I am now preparing to observe forming stars (called protostars) beyond our Solar System, which is an exciting adventure, indeed!

Part I of introducing the Keck observation process discussed some of the interesting aspects of the 10-meter Keck II telescope atop Mauna Kea, including its unique mirror design and one of its instruments, the near-infrared high-resolution spectrograph, or NIRSPEC, which I use with my colleagues to observe carbon monoxide in the gas surrounding protostars. These observations are compared to meteorites and our Sun to help us better understand how our Solar System formed and evolved.

Welcome to Part II! Here I hope to provide  a small window into how observations at the Keck Telescope produce cutting-edge data of solar systems evolving today, before planets can form around their stars:

Astronomical observations using extremely large ground-based facilities is a team effort, involving full-time astronomers who work on the summit of Mauna Kea to help locate scientists’ target stars, and open and close the massive Keck domes. Meanwhile, the observing scientists, located at Keck Headquarters down the mountain, operate the instruments connected to the telescope. Further, there are supporting astronomers at HQ, who help with any software problems during observing, and a team of engineers who help trouble-shoot any number of issues that can arise during the operation of the massive telescope and complex instrumentation.

From starlight to data: The path of light from the telescope mirror to the instrument detectors starts as a reflecting optical telescope, on a very large scale. The light first bounces from the primary, 10-meter mirror to secondary and tertiary mirrors, finally reflecting off of a focal point to the instrument being used.

Keck light path

Light path from Keck mirrors to the science instrument, shown at the left of the image as a blue square. For our project, this instrument would be the near-infrared high-resolution spectrograph (NIRSPEC). (Image from SpacecraftKits.com)

After passing through the prescribed path of in instrument, the light is transformed in such a way that it can later be analyzed. For instance, the light entering NIRSPEC is split into various infrared wavelengths and transformed onto detectors. The spectral images on the detectors can then be processed, or “reduced” into a format that scientists can then further reduce the data for analysis.

NIRSPEC light path

Path of light coming from the Keck telescope through the NIRSPEC instrument, to the detectors. The path begins on the left of the image, and ends on the right (Image from the NIRSPEC Users Manual).

Observing at Headquarters often means operating the software that runs the instrument. My first observing as a graduate student at UCLA was driving NIRSPEC all night, which was simultaneously both nerve-wracking and exciting! These are a few of the main screens used to control the instrument at the telescope:

NIRSPEC instrument control

NIRSPEC instrument control at the computer console. The observer at this console operates various aspects of the instrument using this interface. (NIRSPEC manual, Keck Observatory).

There are two cameras on NIRSPEC, the infrared slit-viewing camera (“SCAM”), which helps in guiding the telescope to the target, and “SPEC”, which takes and stores the images of the spectra, which are the data the scientists will later analyze.

Even with specific stellar coordinates, precisely locating a particular target can be tricky. The SCAM camera acts as a guider, helping the astronomers find their targets. Below are two sample images from our observing run a few years ago, showing a single target (top) and the many stars in a small part of the region near the constellation Orion (bottom).

A stellar target

A stellar target imaged with the SCAM camera guider on the NIRPSEC instrument. (Photo: R. Smith)

Orion

A portion of the Orion nebula seen through the Keck telescope. Orion is comprised of thousands of new and forming stars, and is an excellent area for studying the evolution of solar systems (Photo: R. Smith).

Orion is not only a familiar constellation in the night sky, but is also a giant cloud in which thousands of new stars and planets are forming right now.

Light passing through the spectrograph is split into various components, depending on the settings the scientists want for their research. For observing carbon monoxide, the wavelengths are split as finely as possible to separate the molecules needed for determining abundances in the gas surrounding our target star.

This is one of the spectral images we during our last observing run. Dark lines indicate absorption of light due to molecules in the gas being observed:

A spectral image

A spectral image taken by the NIRSPEC detector. These images are later transformed into spectral lines that can be analyzed. (Image: R. Smith)

Observations of data similar to the image above are stored on a disk which the scientists take to reduce into spectra that can be analyzed. These spectra show the intensity of absorption versus the wavelength corresponding to molecules of interest. Reducing data is a complex process that involves corrections to the spectra from interference of the Earth’s atmosphere, and obtaining accurate measurements of the intensity of the molecular lines in the gas for the astronomical target stars.

Below is an example spectrum from a protostar that was observed by colleagues at the California Institute of Technology. I will be re-observing this protostar  in September. This object is many times more massive than our Sun, and the data from such a protostar will potentially help us understand how the carbon monoxide abundance changes in environments with high Ultraviolet radiation as well as carbon monoxide ice.

These observations should help us better understand of the environment in which our Solar System formed about 4.6 billion years ago.

Spectrum of a massive forming star

(A) Spectrum of the massive protostar, IRAS 19110+1045. This object was observed using NIRSPEC by colleagues in Prof. Geoffrey Blake’s astrochemistry group at Caltech. The spectra in this form have been transformed from the spectral images taken by the NIRSPEC camera, and can now be analyzed. The downward-facing black lines are the amount of light absorbed by carbon monoxide molecules. The bottom panel (B) shows a zoom into one of the regions where 3 “variations” of carbon monoxide are shown. Spectra of this type are analyzed to determine precise abundances of carbon monoxide in the gas surrounding this protostar (Image: R. Smith; Data courtesy of Dr. K. Pontoppidan and Prof. G. Blake).

I am very excited for this next observing run, where we will hopefully obtain data from massive protostars, which can then be compared to our previous work on smaller protostars, with sizes similar to our own Sun. The data below were observed by my colleague at the Space Telescope Science Institute, Dr. Klaus Pontoppidan, using a similar type of spectrograph, the cryogenic high-resolution infrared echelle spectrograph (CRIRES) on the Very Large Telescope in Chile. I analyzed the reduced spectra and obtained chemical abundances for several different forming stellar systems. Example spectra are shown below, where many deep carbon monoxide lines are found:

Spectra of protostellar gas

Spectra of protostellar gas taken with the CRIRES spectrograph. The deep black lines indicate absorption by a “forest” of carbon monoxide gas molecules in a disk of gas (top) and envelope of gas (bottom) surrounding two different forming stars within about 1,500 light-years of our Solar System. These lines were analyzed to determine abundances of carbon monoxide that enables comparison with meteorites and our Sun. (Published in Smith et al., The Astrophysical Journal, 701, 163, 2009)

NOTE! I will be conducting a live video interview from Keck observing HQ during our next run on September 28, 2012, which will be shown in our Daily Planet theater. Stay-tuned for more information! 

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2 Comments leave one →
  1. August 24, 2012 5:35 pm

    Reblogged this on NC Museum of Natural Sciences Blogs and commented:

    by Rachel L. Smith

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