The following are examples of my research activities in the astronomy and
astrophysics of OB star winds:
Figure 1(at left): Model fit to the Si IV 1400 Å doublet in the
B0.5 Ib supergiant HD 64760. The figure shows the two contributions to the
fit: the transmitted (dotted) and scattered (dashed) components (from Massa,
Prinja, & Fullerton 1995).
Figure 2(at right): A dynamic spectrum (the abscissa is velocity
relative to the blue component of the Si IV 1400 Å doublet and time
increases upward) of a 6 day time series of the rapidly rotating B1 Ib star,
gamma Ara. The Spectra are normalized by a minimum absorption (maximum flux)
template, so that all variations appear as absorptions. Notice that
while wind activity extends to roughly -1500 km/s, there is also a
distinct feature moving slowly out to a terminal velocity of less than
-800 km/s. This indicates the presence of a two component, equatorially
compressed, wind (Massa, Prinja, & Fullerton 1996).
A study of FUSE observations of
the winds of early LMC O stars. A particularly interesting result from
this work is a demonstration that the O VI wind doublet is almost certainly
a result of X-ray auger ionization, as first predicted by
Cassinelli & Olsen (1979).
A demonstration of variable ionization in the B supergiant
HD 150168, and other B
I have been interested in the physics of OB star winds for a number of
years. Most recently, I have been collaborating with Prinja and
Fullerton on several studies of wind variability in B supergiant winds.
Some of my work in this field includes:
- Global wind properties
- The discovery of the peculiar
winds in NGC 6231 main sequence B stars (Massa et al. 1984). The
origin of these abnormally strong winds of remains a mystery.
- Determination of the relative
abundances of luminous B stars through the analysis of their wind
lines (Massa et al. 1992). This was one of the first quantitative
derivations of CNO abundances from wind lines and not only quantified
the magnitude of the nitrogen overabundance in the nitrogen rich star
HD 93840, but also suggested that the CNO abundances in normal B
supergiants is normal.
- The cylindrically symmetric wind
of HD 93521 (Massa 1995). This paper provided a unique demonstration
that the wind of HD 93521 in equatorially compressed.
- Wind variability
- I am the PI of a Cycle 6
HST GO program to study the activity of the peculiar winds
of the main sequence B stars in NGC 6231. Theortical arguements
suggest that the flushing time of these winds should be about 20
minutes. The new observations will determine whether this prediction
is accurate, thereby testing radiatively driven stellar wind theory
in a heretofor uncharted region of the HR diagram.
MEGA campaign. I was the PI of this international
collaboration involving 33 scientists. This program monitored the
wind activity in a B supergiant, an O star and a WR star for 16 days
(roughly 3 time the expected rotation period of each star) and
established a causal link between wind variability and rotation in
early type stars.
- The stars selected for the MEGA
program were all, necessarily, rapid rotators, so that several
rotations could be obvserved in 16 days. I was the PI on a
follow up IUE final episode program which monitored the wind
activity of 2 B supergiants with normal rotational velocities.
Although the temporal sampling was not be as dense (one spectrum per
8 hours instead of one per 3 hours in the MEGA), the
baseline is nearly twice as long (28 days) and allowed us to
determine whether wind features repeated from one rotation to the next.
Preliminary results clearly demonstrate
that the wind is also modualted in at least one of the normal stars.
- I am the PI of an ongoing NASA ADP
project which takes advantage of several desirable spectral
diagnostics in B supergiants to follow the temporal evolution of the
mass and ionization structure of their stellar winds. I am also
involved in a NATO exchange program with Raman
Prinja at UC London to expand the scope of this study.
Some relevant publications:
- ``Wind variability of B supergiants: IV. The photospheric connection
in HD 91969'', D. Massa, A.W. Fullerton, R.K. Prinja, I.D. Howarth,
& S.P. Owocki 1997, in preparation
- ``Time-dependent structure in UV absorption lines of the rapid
rotators HD 64760 (B0 Ib) and HD 93521 (O9.5 V)'',
I.D. Howarth, R.H.D. Townsned, M.J. Clayton, A.W. Fullerton, D.R. Gies,
D. Massa, R.K. Prinja, & A.H.N Reid 1997, MNRAS, submitted
- ``Wind variability of B supergiants: III. Corotating spiral
structures in the stellar wind of HD 64760'' A.W. Fullerton, D.L. Massa,
R.K. Prinja, S.P. Owocki, & S.R. Cranmer 1997, A&A, in press
- ``Wind variability of B supergiants: II. The two-component stellar
wind of Gamma Arae'' R.K. Prinja, D. Massa, A.W. Fullerton, I.D. Howarth
& M. Pontefract 1997, A&A, 318, 157
- ``The IUE MEGA Campaign: Wind Variability and Rotation in
Early-Type Stars'' D. Massa, et. al. 1995 ApJ, 452, L53
- ``The IUE MEGA Campaign: Modulated Structure in the Wind of HD
64760 (B0.5 Ib)'' R.K. Prinja, D. Massa, & A.W. Fullerton 1995 ApJ, 452, L61
- ``The IUE MEGA Campaign: The Rotationally Modulated Wind of
zeta Puppis'' I.D. Howarth, R.K. Prinja, & D. Massa 1995 ApJ, 452, L65
- ``Wind Variability in B Supergiants: I. The Rapid Rotator HD 64760
(B0.5 Ib)'', D. Massa, A.Fullerton & R.K. Prinja 1995, ApJ, 452, 842
- ``HD 93521, zeta Oph, and the effects of Rapid Rotation on the
Atmospheres and Winds of O9.5 V Stars'' D. Massa 1995, ApJ, 438, 376
- ``Photospheric Velocity Gradients in B1 Supergiants'', D. Massa, S.N.
Shore & D. Wynne 1992 A&A, 264, 169
- ``Carbon and Nitrogen Abundances in the BN Supergiant HD 93840, and
Their Implications for Normal Galactic Supergiants'', D. Massa, B. Altner,
D. Wynne & H.J.G.L.M. Lamers, 1991 A&A, 242, 188
- ``An Instrument for Optimizing a Space borne Interferometer:
Applications to Calibrating the Cepheid Distance Scale'', D. Massa & A.S.
Endal 1987, AJ, 93, 760
- ``Expected Angular Separations of Late-Type Supergiant + B Star
Binaries in the Milky Way and LMC'', D. Massa & A.S. Endal 1987, AJ, 93,
- ``Main-Sequence B Stars with Strong Winds in the Core of NGC 6231'',
D. Massa, B.D. Savage, & J.P. Cassinelli 1984, ApJ, 287, 814
- ``The influence of Rotation and Stellar Winds upon the Be
Phenomenon'', D. Massa 1975, PASP, 87, 777