George Jacoby

Areas of Interest

Recent Research Results

• Nearby Galaxies
  • Dwarf Galaxies -- With Taft Armandroff , Jacoby and Johns Hopkins student James Davies have found 2 new dwarf galaxies in the Local Group : And V, And VI around M31. Previously, there were only 3 such dwarfs near M31. The first of these, And V, is nearly as faint as any known dwarf galaxy. Both new galaxies were found using the Digital Sky Survey and an innovative digital image processing technique.

  • Planetary Nebulae in M31 -- Jacoby and Robin Ciardullo at Penn State have measured the chemical compositions of 15 planetary nebulae in M31. From these measurements, it is clear that the stars in M31 are derived from a complex history of chemical enrichment because they span a very wide range of compositions, from 20 times lower than the Sun to just slightly higher than the Sun.

  • Planetary Nebulae in Globular Clusters -- Jacoby recently completed a survey for planetary nebulae in the Milky Way globular cluster system. Earlier investigators have failed to find any nebulae, but PN were found in NGC 6441 and Pal 6. The total number of nebulae in the globular cluster system was doubled with the addition of these two. Because the clusters are so poor in planetary nebulae, it seems that the stars must find another path to becoming white dwarfs other than through the PN phase. Since the Sun is only slightly more massive than typical clusters stars (having 85% the mass of the Sun), it is questionable whether the Sun will achieve its promised future of going through a PN phase, as well.

  • Planetary Nebulae in the Galactic Center -- Jacoby and Griet Van De Steene have identified 95 candidate planetary nebulae at the center of our Galaxy. They have obtained follow-up spectra for ~65 of these to confirm all but a couple as bona fide nebulae. The chemical compositions appear to be similar to those found in M31 by Jacoby and Ciardullo.

  • Planetary -- Special Cases -- Jacoby, Gary Ferland of Kentucky, and Kirk Korista of Western Michigan studied the ionization structure of Abell 39 in detail. This nebula is almost perfectly spherical - quite unusual.

  • Sakurai's Star -- Jacoby, Orsola De Marco and Dave Sawyer of WIYN have been following the stellar evolution gyrations of Sakurai's star, a former PN central star that has ejected another shell of material and dust. See: IAU Circulars 7065 and 7155 .

• Distant Galaxy Systems
  • Stars Between the Galaxies -- With Robin Ciardullo and John Feldmeier , Jacoby has been exploring the population of stars between galaxies in the Fornax and Virgo clusters of galaxies. Remarkably a significant fraction of the stars and light in a cluster come from the regions between galaxies, perhaps as much as 50% of the entire cluster light is NOT in galaxies.

Future Research Plans

• Stellar Dynamics
  • Virgo Intracluster PN -- We have been using the WIYN observatory and the ESO VLT to obtain velocities of the PN between the galaxies in Virgo. The observation and analysis of planetary nebula motions in galaxies is of growing interest because there is no better way to measure the stellar velocities, especially for these very faint stars in Virgo. The velocities will map out the distribution and quantity of dark matter in the Virgo cluster far better than the galaxies because there are hundreds of thousands of PN and only a few hundred galaxies.

  • M31 -- Jacoby, Holland Ford, Xaoihui Hui, and Robin Ciardullo have accumulated velocities for over 800 nebulae in the nearby Andromeda galaxy, and the analysis is underway. Preliminary results show that the bulge of the galaxy is rotationally supported. Also, there are about 10 times fewer stars in the galaxy halo that produce planetary nebulae than initially thought, possibly evidence for either a very low mass or a very old halo. Nevertheless, there seem to be several times more halo PN in M31 than in our own Galaxy.

  • Galactic Center -- The observations of the Galactic center nebulae will help define the motions of stars in the central "bar" of our Galaxy, as well as flagging any nebulae that originated in the halo of our Galaxy but are presently passing near the Galactic nucleus; already, two very fast moving candidates have been identified as possible halo visitors.

• Chemical Compositions
  • The Galactic Center -- Thus far, only ~12 of the new ~90 PN in the Galactic center have been analyzed to derive their chemical compositions. In most of the remaining cases, it will not be possible to make the measurements because the nebulae are extremely faint, being extinguished by an enormous of dust between the Galactic center and the Earth. Thus, each nebula that can be studied is an important one. We are continuing our analysis of the existing spectra.

  • M31 Nebulae -- The PN in M31 generally have chemical compositions that are not as enriched as the Sun, even relatively close to the nucleus of the galaxy. This result is in conflict with estimates from spectra of the combined light from the stars in M31 which suggest that the composition of the M31 stars should be greater than that of the Sun. Are the differences in derived compositions due to the methodologies (nebula vs stellar)? Is there some physical reason why enriched stars cannot make planetary nebulae that we then can study? These and other explanations have been explored by Jacoby and Ciardullo, but their sample of 15 nebulae is not very exhaustive. Future studies will target many more PN in M31.

  • The Small Magellanic Cloud -- With Orsola De Marco, Jacoby is planning a significant search campaign for the faintest planetary nebulae in the SMC. The stars in the SMC have very low chemical compositions, nearly one-tenth that of the Sun. Thus, those stars provide an excellent test area for processes that may depend on the metallicities of stars. For example, we will measure the strengths of the winds coming off the PN central stars to see if they are, in fact, weaker than those in our Galaxy.

• Dwarf Galaxies -- Simulations predict that there should be ~1000 dwarf galaxies in our Local Group. We know of about 20. Have the surveys been so poorly executed that most of those galaxies have not been recovered? With Taft Armandroff and summer student Jacqueline Chen, Jacoby will be surveying more and more of the sky to look for the missing dwarfs.

Service

• IRAF -- Image Reduction and Analysis Facility -- Jacoby is the project scientist for the IRAF project, setting priorities and giving scientific direction to the project, interfacing between the programmers and the users, NOAO management, and outside organizations interested in the project (STScI, AXAF, EUVE), and is the PI for the Open IRAF initiative being funded by NASA.

• CCD Mosaic -- Jacoby is one of the project scientists for the CCD Mosaic Camera . In addition, he was the scientist responsible for the new optical correctors recently built for the 4-m and 0.9-m that are required to provide the very wide fields of views (50' and 80', respectively) needed by the Mosaic.

• ADASS Conferences -- Jacoby serves as a member of the scientific organizing committees for the annual Astronomical Data Analysis and Software Systems conferences.

• IAU Symposia on Planetary Nebulae -- Jacoby is a member of IAU Commission 34 (Interstellar Matter) and the Planetary Nebula Working Group. He has been a member of the scientific organizing committees for the Symposia for the past several meetings.

• SWIFT : The Spectroscopic WIde-Field Telescope -- With Arjun Dey, Joan Najita, Sam Barden, and Chuck Claver, Jacoby has been developing the plans for a new national facility that will be able to collect many thousands of spectra of stars and galaxies in each exposure.

• Bilbiography
• Current CV