The Virginia Tech Spectral-Line Survey
Arcminute-Resolution Digital Images of Interstellar
H-alpha and [SII] Emission
Image Specifications |
Image Types, Sky Coverage |
Download Images |
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*** Latest mosaic of Taurus-Orion-Monoceros region ***
The VTSS is a
wide-field image survey of the Galaxy's warm ionized interstellar medium
(WIM, a 10,000 K plasma). The instrumentation used is the Virginia
Tech Spectral Line Imaging Camera (SLIC),
specially designed for obtaining sensitive, arcminute-resolution,
10-degree wide images of the 6563Å H-alpha
recombination line of hydrogen, and the [SII]6717,6731Å
doublet emission of singly ionized sulfur.
This survey will cover the northern hemisphere (declinations greater
than -15 degrees).
The results bear upon studies of, for example,
Survey images are available for downloading from this site. The
images are in FITS format
(Flexible Image Transport System). They can be viewed or analyzed
in programs such as
(a free unix-based professional astronomical image processing program),
(a free FITS viewer in Unix, Windows, or Macintosh versions), or
(a web-based astronomical image processing Java program
that runs through your browser).
If you use any images for
research or other purposes, we request that you use this acknowledgement.
the general ISM phenomena (the distribution of the WIM,
relation to other phases, "supershells," "chimneys," and other
dynamical features, ionization and heating of the interstellar medium,...),
radio wave scattering by the interstellar medium (caused by the
searches for small-scale anisotropies in the cosmic
microwave background radiation produced in the Big Bang.
(Irregularities in the foreground, microwave-emitting Galactic
plasma mimic irregularities in the background radiation.)
The survey consists of a set of wide-field images with the following specifications:
- Each digital image is circular, with a 10-degree diameter.
- Pixels are 1.6 arcminutes in width.
- The image sensitivity allows detection of sub-Rayleigh
intensity structures (1 Rayleigh = 1 R = 10/4
photons per square centimeter per second per steradian, corresponding
to an emission measure of about 2 pc/cm in
an H-alpha image).
- The median intensity in each FITS image has been set equal to zero.
Image Types, Sky Coverage
There will be four images available for each field: H-alpha,
[SII], Continuum-Corrected H-alpha, and Continuum-Corrected
[SII]. The Continuum-Corrected H-alpha and [SII] images are produced
by a process including the alignment and subtraction of a suitably scaled
version of a continuum image from the H-alpha or [SII] image.
(Continuum images are taken with a wide-bandpass filter, or a
double-bandpass filter straddling the H-alpha line or [SII] doublet.)
Observations were generally conducted first near the galactic plane proceeding
to higher latitudes. Imaging in [SII] was commenced well after many H-alpha
observations were complete. Images are made available at this website as
they are processed.
Field images are made available for download as they are processed. A
field's name consists of the three letter abbreviation of the
constellation where the field center lies, plus a two digit number
(e.g., Cyg13). The coordinates for field centers provided in the
following lists and image maps are approximate epoch 2000.0 coordinates.
(An accurate coordinate specification is included
in the FITS file header for each image). Each image is 10-degrees in
diameter. If you use any images for research or other purposes, we request
that you use this acknowledgement.
Check the availability of images and download them using:
or search for the correct field for a specific position of interest:
The following clickable image maps can be used to check which images are
currently available within 30 degrees of the galactic plane, and download them.
The maps show the 10-degree wide
circular fields that have been observed. The rectangular grid lines
display galactic coordinates; lines of constant right ascension are
shown as dashed lines (at 3h separations), and a dotted line
shows the lower declination limit of the survey (-15 degrees). When you
move your mouse cursor over a field, information about the field will
appear in your browser's status line, or in a small text display near
the cursor (after a momentary delay), depending upon your browser.
Images available are listed by number: 1=H-alpha, 2=[SII],
3=Continuum-Corrected H-alpha, 4=Continuum-Corrected [SII].
Click on a field to download any of its images.
Mosaics, created from sets of our
images, are available for viewing.
People who are working (or have worked) on this project are listed below.
- John Simonetti
- Brian Dennison
- Phil Nelson (Graduate Student)
- Ken Portock (Former Graduate Student, MS 2002)
- Gregory Topasna (Former Graduate Student, PhD 1999; Faculty Member, Virginia Military Institute)
- Jennifer Beard (Fromer Undergraduate Student, Graduate Student)
- Richard Foster (Undergraduate Student)
- Carol Thornton (Former Undergraduate Student)
- James Lough (Former Undergraduate Student)
- Mark Blackmon (Former Undergraduate Student)
- Adam Drake (Former Undergraduate Student)
- Carter Hall (Former Undergraduate Student)
- Caitlin Kelleher (Former Undergraduate Student)
- Jason Rufner (Former Undergraduate Student)
- Mark Wallace (Former Undergraduate Student)
This work is supported by National
Science Foundation grants AST-9319670, AST-9800476, and AST-0098487,
and by the Horton Foundation.
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