This is the annual status report for the third year of our LTSA grant 'Open Clusters as Laboratories.' Because we have now had a few years to work on the project, we have started to produce and publish a large number of papers. We have been extremely successful in obtaining ROSAT observations of open clusters. With the demise of the PSPC on ROSAT, our main data source has come to an end and we will be able to concentrate on analyzing those data

Stauffer, John R.

English

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_ _I_R MOMENTUM EVOLUTION OF YOUNG STARS
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Grant NAGW-2698
Annual Status Report No. 2
For !he period 1 May 1993 through 30 April 1994
Principal Investigator:
Dr. John R. Stauffer
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March 1994
Prepared for
National Aeronautics and Space Administration
Washington, D.C.
Smithsonian Institution
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Officer for this grant is Dr. G. Riegler, Science Operations
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https://ntrs.nasa.gov/search.jsp?R=19950004167 2020-06-16T11:48:16+00:00Z

Open Clusters as Laboratories:
The Angular Momentum Evolution of Young Stars
Grant NAGW-2698
Annual Status Report No. 2
This is the annual status report for the third year of our LTSA grant "Open Clusters as
Laboratories." Because we have now had a few years to work on the project, we have started
to produce and publish a large number of papers. We have been extremely successful in ob-
taining ROSAT observations of open clusters. With the demise of the PSPC on ROSAT, our
main data source has come to an end and we will be able to concentrate on analyzing those
data. We look forward to the planned launch of ISO in Fall 1995 since data from that mis-
sion should provide us with additional observational data needed to model the PMS angular
momentum evolution of low mass stars.
Our main Pleiades ROSAT PSPC paper has now been published, and we are working on a
second paper which will be devoted to analysis of the X-ray flares and long-term variability of
Pleiades members. A set ofROSAT HRI observations are in progress that will provide us
with high resolution X-ray images of selected regions in the Pleiades which we decided were
necessary in order to separate a number of regions where several sources are blended to-
gether.
Our main HST WFPC Trapezium cluster luminosity function paper has been published re-
cently, and we have just submitted two followup papers which estimate the fraction of
Trapezium cluster members with protoplanetary circumstellar disks and provide near-in-
frared photometry for the Trapezium cluster members. A fourth paper where we will provide
spectral types and reddening estimates and use those data to estimate the stellar mass func-
tion for the Trapezium cluster is in progress.
We have just submitted a paper on ROSAT HRI observations of the high mass stars in the
Orion/Trapezium cluster whose purpose was to determine whether the late-B and early-A
type stars there are intrinsic X-ray sources (as had been claimed in the literature) or if in-
stead their X-ray emission is more likely attributable to low mass binary companions. We
favor the latter interpretation in our paper. A long-awaited complete reanalysis of the
EINSTEIN Orion observations has been written by one of us, with submission to the journal
expected shortly.
Our collaborators in Germany (J. Schmitt and S. Randich) have completed analysis of the
ROSAT raster-scan data for Praesepe; nearly completed analysis of the raster data for
IC2602; and will soon start final analysis of the raster-scan data for the Alpha Per cluster.
We have been working on obtaining optical data for the X-ray sources identified in the
ROSAT data. In particular, we have obtained and analyzed an extremely large amount of
CCD imaging data for IC2602, which has allowed us to provide optical ID's and photometry
for about 30 of the IC2602 X-ray sources. An observing run to obtain spectra of the IC2602
low mass X-ray sources is scheduled for April 1994.
New pointed ROSAT PSPC observations of NGC6475 and the Alpha Persei cluster have been
obtained and analyzed during this period. Basic analysis of both sets of data has been com-
pleted. We also obtained a large CCD mosaic of NGC6475, and have used those data to de-
termine optical identifications of cluster member X-ray sources (in the same manner as was
done for IC2602).
Analysis of the Hyades ROSAT X-ray data continues, with two more papers submitted dur-
ing the period covered by this report: the first paper provides an analysis of the dK and dM
-1-
Hyades members detected in pointed ROSAT observations, and the second paper is devoted
to an analysis of the complete ROSAT survey data for the Hyades. A paper on chromospheric
activity of very low mass Hyades and Pleiades members was also submitted during the pe-
riod.
A new set of spotted star light curve data for Pleiades, Hyades, and Alpha Persei members
was obtained during the last observing season. A small amount of additional data is ex-
pected to be obtained during a March 1994 observing run. Initial analysis of the main
dataset indicates that we should be able to derive new rotation periods for most of the stars
we have observed.
tCB. MacGregor continued development of theoretical models of the angular momentum
evolution of low mass stars. The latest version of the models (described in a paper just sub-
mitted to Astronomy and Astrophysics) incorporates disk-regulated PMS rotation - a newly
predicted facet of the evolution of these stars that may provide the key to interpreting the
distribution of rotational velocities and X-ray emission for stars in our young open clusters.
One of us (J.-P. Caillault) was the host to the 8th Cool Stars and Stellar Systems conference
held in Athens, Georgia, in October 1993. Several members of the team attended the meet-
ing and gave review talks. A team meeting was held during one evening at the meeting.
Our plans for the next year of the LTSA project remain essentially unchanged from our
original proposal. Since we will have finished analysis of all the ROSAT PSPC data, we will
be able to do correlation studies of X-ray activity vs. age and mass. We will also be involved
in ground-based studies to determine the optical properties of the X-ray sources. The AO for
U.S. participation in the ISO mission will be issued in the next few months, and we plan to
submit one or more proposals to search for disks around low mass stars in our primary open
clusters.
Papers published or submitted for publication during the period:
Ayres, T.R., Stauffer, J.R., Simon, T., Stern, R.A., Antiochos, S.K., Basri, G.S., Bookbinder,
J.A., Brown, A., Doschek, G.A., Linsky, J.L., Ramsey, L.W., and Walter, F.M. 1994, A Far-
Ultraviolet Flare on a Pleiades G Dwarf, ApJ 420, L33.
Caillault, J.-P., Gagn_, M., and Stauffer, J.R., ROSAT HRI Observations of Hot Stars in the
Orion Nebula, ApJ, submitted.
Hamilton, D., and Stauffer, J.R. 1993, Optical Spectroscopy of Very Low Mass Stars in the
Pleiades, AJ 105, 1855.
McCaughrean, M., and Stauffer, J.R. High Resolution Near-Infrared Imaging of the
Trapezium Cluster: A Stellar Census, AJ, submitted.
Prosser, C.F., Shetrone M.D., Marilli, E., Catalano, S., Williams, S.D., Backman, D.E.,
Laaksonen, B.D., Adige, V., Marschall, L.M., and Stauffer, J.R. 1993, Rotation Periods of
Open Cluster Stars. II., PASP 105, 1407.
Prosser, C.F., Stauffer, J.R., Hartmann, L., Soderblom, D.R., Jones, B.F., Werner, M.W., and
McCaughrean, M.J. 1994, HST Photometry of the Trapezium Cluster, ApJ 421, 517.
Prosser, C.F., and Giampapa, M.S. 1994, A Radial Velocity Survey of the Open Cluster IC
4665, AJ, submitted.
-2-
Prosser,C.F.1994,PhotometryandSpectroscopyin theOpenClustera Persei. II, AJ, April
issue.
Pye, J.P., Hodgkin, S.T., Stern, R.A., and Stauffer, J.R. 1994, ROSAT X-Ray Luminosity
Functions of the Hyades dK and dM Stars, MNRAS March issue.
Schmitt, J., Kahabka, P., Stauffer, J.R., and Piters, A.J.M. 1993, ROSAT All Sky X-Ray
Survey of the Core of the Pleiades Cluster, A&A 277, 114.
Soderblom, D.R., Stauffer, J.R., MacGregor, I_B., and Jones, B.F. 1993, The Evolution of
Angular Momentum Among Zero-Age Main Sequence Stars, ApJ 409, 624.
Soderblom, D.R., Fedele, S.B., Jones, B.F., Stauffer, J.R., and Prosser C.F. 1993, The
Evolution of the Lithium Abundances of Solar-Like Stars. IV. Praesepe, AJ 106, 1080.
Soderblom, D.R., Jones, B.F., Balachandran, S., Stauffer J.R. 1993, The Evolution of the
Lithium Abundances of Solar-Like Stars. III. The Pleiades, AJ 106, 1059.
Stauffer, J.R., Prosser, C.F., Soderblom, D.R., and Simon T. 1993, Lithium and
Chromospheric Activity in the Alpha Persei Cluster, AJ 106, 229.
Stauffer, J.R., Caillault, J.-P., Gagn_, M., Prosser, C.F., and Hartmann, L. 1994, A Deep
Imaging Survey of the Pleiades with ROSAT, ApJ Supp. 91, 625.
Stauffer, J.R., Liebert, J., Giampapa, M., Macintosh, B., Reid, N., and Hamilton, D. 1994,
Radial Velocities of Very Low Mass Stars and Candidate Brown Dwarf Members of the
Pleiades and Hyades, AJ, accepted.
Stauffer, J.R., Hartmann, L., Prosser, C.F., and McCaughrean, M. 1994, Additional HST
Observations of EIDERS in the Trapezium, AJ, submitted.
Stauffer, J.R., Hamilton, D., and Probst, R.G. 1994, A CCD-Based Search for Very Low Mass
Members of the Pleiades Cluster, AJ, accepted
Stauffer, J.R., Prosser, C.F., Hartmann, L., and McCaughrean, M.J., Additional Constraints
on Circumstellar Disks in the Trapezium Cluster, AJ, submitted.
Stern, R.A., Schmitt, J., Pye, J.P., Hodgkin, S.T., Stauffer, J.R., and Simon, T. 1994, Coronal
X-Ray Sources in the Hyades: A 40 ksec ROSAT Pointing, ApJ, June issue.
Stern, R.A., Schmitt, J., and Kahabka, P. The Complete ROSAT Survey of the Hyades, ApJ,
submitted.
Vrba, F.J., Chugainov, P.F., Weaver, W.B., and Stauffer, J.R. 1993, Photometric and
Spectroscopic Monitoring ofAA Tau, DN Tau, UX Tau A, T Tau, RY Tau, LkCa 4 and LkCa
7, AJ 106, 1608.
-3-



Open clusters as laboratories: The angular momentum evolution of young stars

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