2WoRLDS -- 2MASS Wolf-Rayet Line Detection Survey

or "Crouching Galaxy, Hidden Stars"

2WoRLDS, The 2MASS Wolf-Rayet Line Detection Survey is a dedicated imaging and spectroscopic campaign aimed at discovering new populations of Wolf-Rayet (WR) stars in the Galaxy.

Update: Fall, 2005

Update: Fall, 2004

History

Wolf-Rayet (WR) stars were discovered in 1867 by Mssrs. Wolf and Rayet during routine visual spectroscopic surveys at the Observatoire de Paris. They found the extremely bright lines they saw in the spectra (incomparably the most brilliant and striking in the whole heavens -- R. Copeland, 1883) impossible to identify. Helium, the element responsible for most of these strong features, was not identified in spectra of the solar corona until the following year.

Background

It is now known that WR stars represent an evolved state of the most massive stars (>25 solar masses). During the final 10% of massive O-stars' short lifetimes, before exploding as a supernova, many undergo a period of steady, extreme mass loss. During this time, one solar mass is ejected in a fast wind (up to 5000 km/s) every 10,000-100,000 years. This is about 10 orders of magnitude larger than the solar wind!

WR stars are extremely important in models of starburst populations. In young bursts of star formation, they can contribute to the ISM as much kinetic energy and metal enrichment as supernovae, and can completely dominate the far-UV output below the helium Lyman limit. Since they have such short duration, and occur at a fairly well-known time in a massive star's lifetime, they act as excellent chronometers. They are also sensitive metallicity indicators, and are interesting in their own right as laboratories for extreme stellar evolution, mass loss, and nuclear processing.

How Many & Where

There are currently only 230 known Galactic WR stars. While they are rare objects, as are all massive stars, models predict around 2500 should exist in the Galaxy. Since they are so bright (10,000,000 times as bright as the sun!) there is no problem seeing them at great distances. The difficulty comes from their location. Like most massive stars, the young WR stars haven't had time to move away from their birthplace in the disk of the Galaxy. In fact, all but a handful of WR's are located within 5 degrees of the Galactic plane. The plane contains copious quantities of dust which extincts optical wavelengths, imposing about 1.5 magnitudes of extinction every 1 kpc. Despite the extreme luminosities of these stars, they can only be seen relatively nearby.

A good way to find WR stars, then, is to use infrared wavelengths, which do not suffer as much from the extincting effects of dust. This survey will capitalize on an existing search technique which makes use of the broadband near-infrared J, H, & Ks colors of the 2MASS all-sky survey to find promising WR candidates. High density regions of candidate WR stars (most of which will not, in fact, be WR's, but other contaminants, like red giant stars, planetary nebulae, or carbon stars) will be selected.

A special set of K-band line filters has been comissioned to match the broad, strong infrared emission lines which characterize WR stars.

Strategy

The search strategy will consist of three parts:

1. Query 2MASS point sources in specific regions along the Galactic Plane, applying custom color cuts to find promising fields. Supplement with 2MASS-selected clusters.
2. Use Pisces, a near-infrared imager on the Steward 90" telescope (Kitt Peak), and MMT (Mt. Hopkins), to obtain 5 band imaging in the special filter set.
3. Using CorMASS, a near infrared spectrograph on the VATT (Mt. Graham, seen at right) or APO telescopes obtain zJHK low-resolution spectroscopy of the candidates identified in the line images to identify new WR stars!

Opportunity & Status

2WoRLDS provides ample opportunities to be involved with a wide variety of observational, database/catalog, and data reduction & interpretation techniques, including:

• Observing when the moon is up (for those optical astronomers among you).
• Catalog searching and selection.
• Infrared narrow-band imaging.
• Near-infrared spectrocopy.
• Object recognition and registration, and synthetic aperture photometry.
• Reduction and extraction of cross-dispersed infrared spectra.
• IR classification and spectral interpretation.

Many of the selection and candidate identification details are still being worked out, so there is still abundant opportunity to have a significant impact on the overall program.

For the interested, a copy of the proposal is available. Please feel free to email me or stop by Rm. 326.