Steven Federman (Interstellar Matter)
Professor of Astronomy
Ph.D., 1979, New York University
Dr. Federman uses spectroscopy as the means to study the physical environment
of interstellar gas clouds. Star formation takes place in these clouds,
and by studying the physical environment of the clouds, a better understanding
of the processes involved in star formation is possible. Another area of
interest involves isotopic ratios, such as 7Li/6Li, 11B/10B,
and 85Rb/87Rb, and seeks a better understanding of the
sites where these elements are produced by nuclear reactions. He makes many of
his measurements with telescopes at McDonald Observatory in West Texas,
with the Hubble Space Telescope, and
with the Far Ultraviolet Spectroscopic
Explorer or FUSE.
Measurements of atomic and molecular abundances in interstellar clouds allow a determination of gas density and
temperature. In order to extract information on density and temperature, Dr.
Federman conducts two types of analyses. In one case, he examines relative
populations among energy levels in the C2 molecule and neutral atomic
carbon. The other technique is based on the chemical network that connects the
production of CN with the abundances of CH and C2. These analyses reveal that typical densities are 100-400 atoms (and
molecules) per cubic centimeter and typical temperatures are 40-60 K.
The research on isotopic ratios is focused on determining the importance of
three processes, cosmic ray spallation, neutrino spallation, and neutron
capture. Spallation involves the breaking apart of nuclei resulting from a
collision. Cosmic ray spallation occurs when relativistic protons and helium
nuclei travel through our Galaxy and collide within interstellar carbon,
nitrogen, and oxygen. This process plays a role in the production of the light
elements, Li, Be, and B. Neutrino spallation takes place in supernova explosions
associated with the death of stars 10 or more times more massive than the Sun.
Here, the neutrinos break apart helium, carbon, and neon nuclei and in the
process synthesize 7Li, 11B, and 19F (the sole
stable isotope of fluorine). Neutron capture also occurs in asymptotic giant
branch stars, massive stars undergoing helium and carbon fusion, and supernova
explosions involving the death of a massive star; the rubidium isotopes probe
this type of nuclear reaction.
To study these and other atomic/molecular species,
one requires accurate laboratory absorption cross sections (or transition
probabilities). The data yield oscillator strengths that are especially relevant
for our astronomical studies. In many instances, the interstellar spectra provide the
first accurate measurements. In a related laboratory program, Dr. Federman is collaborating
with Dr. Schectman on the determination of ultraviolet
oscillator strengths
for atoms of interest to interstellar studies and with colleagues at Toledo (Dr.
Cheng) and in France on cross sections for CO. Facilities used in this
research include the Toledo Heavy Ion Accelerator , the Synchrotron
Radiation Center of the University of Wisconsin-Madison, and the LURE
synchrotron in Orsay, France. Future plans include measurements taken at
SOLEIL, a
third generation synchrotron in France.
A sampling of my publications is given below, grouped by topic -- structure
and chemistry of interstellar clouds, CO photochemistry, production of the elements, and
atomic oscillator strengths.
Structure and Chemistry of Interstellar Clouds:
- Y. Sheffer, and S.R. Federman, "Hubble Space Telescope Measurements
of Vacuum Ultraviolet Lines of Interstellar CH," Ap. J. 659, 1352 (2007).
(PDF)
- A.M. Ritchey, M. Martinez, K. Pan, S.R. Federman, and D.L. Lambert, "The
Nature of Interstellar Gas toward the Pleiades Revealed in Absorption Lines,"
Ap. J. 649, 788 (2006).
(PDF)
- D.E. Welty, S.R. Federman, R. Gredel, J.A. Thorburn, and D.L. Lambert, "VLT
UVES Observations of Interstellar Molecules and Diffuse Bands in the
Magellanic Clouds," Ap. J. Suppl. 165, 138 (2006).
(PDF)
- K. Pan, S.R. Federman, Y. Sheffer, and B-G Andersson, "Cloud
Structure and Physical Conditions in Star-forming Regions from Optical
Observations. II. Analysis," Ap. J. 633, 986 (2005).
(PDF)
- K. Pan, S.R. Federman, K. Cunha, V.V. Smith, and D.E. Welty, "Cloud
Structure and Physical Conditions in Star-forming Regions from Optical
Observations. I. Data and Component Structure," Ap. J. Suppl. 151, 313
(2004). (PDF)
- J. Zsargó, and S.R. Federman, "Nonthermal Chemistry in Diffuse Clouds
with Low Molecular Abundances," Ap. J. 589, 319 (2003). (PDF)
- E. Rollinde, P. Boissé, S.R. Federman, and K. Pan, "Small Scale
Structure in Molecular Gas from Multi-epoch Observations of HD 34078,"
Astron. and Ap. 401, 215 (2003). (PDF)
- K. Pan, S.R. Federman, and D.E. Welty, "Density Variations over
Subparsec Scales in Diffuse Molecular Gas," Ap. J. (Letters) 558, L105
(2001). (PDF)
- D.C. Knauth, S.R. Federman, K. Pan, M. Yan, and D.L. Lambert, "Physical
Conditions in the Foreground Gas of Reflection Nebulae: NGC 2023, vdB 102,
and NGC 7023," Ap. J. Suppl. 135, 201 (2001). (PDF)
- M. Yan, S.R. Federman, A. Dalgarno, and J.E. Bjorkman, "Theoretical
Modeling of ISO Results on Planetary Nebula NGC 7027," Ap. J. 515, 640
(1999). (PDF)
- S.R. Federman, D.C. Knauth, D.L. Lambert, and B.-G. Andersson, "Probing
the Photodissociation Region toward HD 200775," Ap. J. 489, 758 (1997).
(PDF)
- S.R. Federman, D.E. Welty, and J.A. Cardelli, "The Amount of CH
Produced during CH+ Synthesis in Interstellar Clouds," Ap.
J. 481, 795 (1997). (PDF)
- S.R. Federman, J. Weber, and D.L. Lambert, "Cosmic Ray Induced
Chemistry toward Perseus OB2," Ap. J. 463, 181 (1996). (PDF)
- S.R. Federman, J.M.C. Rawlings, S.D. Taylor, and D.A. Williams, "Synthesis
of Interstellar CH+ without OH," M.N.R.A.S. 279, L41 (1996).
(PDF)
-
S.R. Federman, J.A. Cardelli, E. F. van Dishoeck, D.L. Lambert,
and J.H. Black, "Vibrationally Excited H2, HCI and NO+ in Diffuse Clouds
toward z Ophiuchi," Ap. J. 445, 325, (1995). (PDF)
-
D.L. Lambert, Y. Sheffer, and S.R. Federman, "Hubble Space
Telescope Observations of C2 Molecules in Diffuse Interstellar Clouds," Ap. J. 438, 740 (1995).
(PDF)
- S.R. Federman, C.J. Strom, D.L. Lambert, J.A. Cardelli, V.V. Smith,
and C.L. Joseph, "Chemical Transitions for Interstellar C2 and CN in
Cloud Envelopes," Ap. J. 424, 772 (1994). (PDF)
- G. Crinklaw, S.R. Federman, and C.L. Joseph, "The Depletion
of Calcium in the Interstellar Medium," Ap. J. 424, 748 (1994). (PDF)
- J.A. Cardelli, S.R. Federman, and V.V. Smith, "Interstellar
Environments Probed by Ca I
Absorption and the Effects of Density-dependent Depletions," Ap. J.
(Letters) 381, L17 (1991). (PDF)
CO Photochemistry:
- M. Eidelsberg, Y. Sheffer, S.R. Federman, J.L. Lemaire, J.H. Fillion, F.
Rostas, and J. Ruiz, "Oscillator Strengths and Predissociation Rates for
Rydberg Transitions in
12C16O, 13C16O and 13C18O
Involving the E 1P,
B 1S+,
and W 1P
States," Ap. J. 647, 1543 (2006).
(PDF)
- M. Eidelsberg, J.L. Lemaire, J.H. Fillion, F. Rostas, S.R. Federman, and
Y. Sheffer, ''Oscillator Strengths for Transitions to Rydberg Levels in
12C16O, 13C16O and 13C18O
between 967 and 972 Å," Astron. and Ap. 424, 355 (2004).
(PDF)
- T. Crenny, and S.R. Federman, "Reanalysis of Copernicus
Measurements on Interstellar Carbon Monoxide," Ap. J. 605, 278 (2004).
(PDF)
- Y. Sheffer, S.R. Federman, and B.-G. Andersson, "FUSE Measurements of
Rydberg Bands of Interstellar CO between 925 and 1150 Å," Ap. J.
(Letters) 597, L29 (2003). (PDF)
- S.R. Federman, D.L. Lambert, Y. Sheffer, J.A. Cardelli, B.-G. Andersson,
E.F. van Dishoeck, and J. Zsargó, "Further Evidence for Chemical
Fractionation from Ultraviolet Observations of Carbon Monoxide," Ap. J.
591, 986 (2003). (PDF)
- Y. Sheffer, D.L. Lambert, and S.R. Federman, "Ultraviolet Detection
of Interstellar 12C17O and the CO Isotopomeric Ratios toward X Per," Ap.
J. (Letters) 574, L171 (2002). (PDF)
- Y. Sheffer, S.R. Federman, and D.L. Lambert, "High-resolution
Measurements of Intersystem Bands of Carbon Monoxide toward X Persei,"
Ap. J. (Letters) 572, L95 (2002). (PDF)
- S.R. Federman, M. Fritts, S. Cheng, K.L. Menningen, D.C. Knauth, and K.
Fulk, "Oscillator Strengths for B - X, C - X, and
E - X Transitions in
Carbon Monoxide," Ap. J. Suppl. 134, 133 (2001). (PDF)
- S.R. Federman, K.L. Menningen, W. Lee, and J.B. Stoll, "Relative Band Oscillator
Strengths for Carbon Monoxide: A 1P -
X 1S+ Transitions,"
Ap.
J. (Letters) 477, L61 (1997). (PDF)
- D.L. Lambert, Y. Sheffer, R.L. Gilliland, and S.R. Federman, "Interstellar
Carbon Monoxide toward z Ophiuchi," Ap. J. 420, 756 (1994).
(PDF)
Production of the Elements:
- S.R. Federman, Y. Sheffer, D.L. Lambert, and V.V. Smith, "Far
Ultraviolet Spectroscopic Explorer Measurements of Interstellar
Fluorine,'' Ap. J. 619, 884 (2005). (PDF)
- S.R. Federman, D.C. Knauth, and D.L. Lambert, "The Interstellar
Rubidium Isotope Ratio toward r Ophiuchi A,"
Ap. J. (Letters) 603, L105 (2004). (PDF)
- D.C. Knauth, S.R. Federman, and D.L. Lambert, "An
Ultra-high-resolution Survey of the Interstellar 7Li-to-6Li
Isotope Ratio in the Solar Neighborhood, " Ap. J. 586, 268 (2003);
erratum, Ap. J. 594, 664 (2003). (PDF)
- D.C. Knauth, S.R. Federman, D.L. Lambert, and P. Crane, "Newly
Synthesized Lithium in the Interstellar Medium," Nature 405, 656
(2000).
- D.L. Lambert, Y. Sheffer, S.R. Federman, J.A. Cardelli, U.J. Sofia, and
D.C. Knauth, "The 11B/10B Ratio of Local
Interstellar Diffuse Clouds," Ap. J. 494, 614 (1998). (PDF)
- S.R. Federman, D.L. Lambert, J.A. Cardelli, and Y. Sheffer, "The
Boron Isotope Ratio in the Interstellar Medium," Nature 381, 764 (1996).
Atomic Oscillator Strengths:
- L.J. Curtis, S.R. Federman, S. Torok, M. Brown, S. Cheng, R.E. Irving, and
R.M. Schectman, "The Need for Branching Fraction Measurements in
Multiply-charged Ions," Phys. Scr., 75, C1 (2007).
(PDF)
- S.R. Federman, M. Brown, S. Torok, S. Cheng, R.E. Irving, R.M. Schectman,
and L.J. Curtis, "Oscillator Strengths for Ultraviolet Transitions in
P II,"
Ap. J. 660, 919 (2007).
(PDF)
- R.M. Schectman, S.R. Federman, M. Brown, S. Cheng, M.C. Fritts, R.E.
Irving, N.D. Gibson, "Oscillator Strengths for Ultraviolet Transitions in Cl
II and
III,'' Ap. J. 621, 1159 (2005).
(PDF)
- S.R. Federman, and J. Zsargó, "Atomic Physics with the
Goddard High Resolution Spectrograph on the Hubble Space Telescope. V. Oscillator
Strengths for Neutral Carbon Below 1200 Å," Ap. J. 555, 1020 (2001). (PDF)
- R.M. Schectman, S. Cheng, L.J. Curtis, S.R. Federman, M.C. Fritts, and R.E.
Irving, "Lifetimes Measurements in Sn II,"
Ap. J. 542, 400 (2000). (PDF)
- C.E. Theodosiou, and S.R. Federman, " Accurate Calculation of Mg II
3s-np Oscillator Strengths," Ap. J. 527, 470 (1999). (PDF)
- E. Biémont, H.P. Garnir, S.R. Federman, Z.S. Li, and S. Svanberg, "Lifetimes
and Oscillators Strengths for Ultraviolet Transitions in Neutral Sulfur,"
Ap. J. 502, 1010 (1998). (PDF)
- K.L. Mullman, J.E. Lawler, J. Zsargó, and S.R. Federman, "Absolute
Vacuum Ultraviolet Oscillator Strengths in Co II
and the Interstellar Cobalt Abundance," Ap. J. 500, 1064 (1998). (PDF)
- J. Zsargó, and S.R. Federman, "Atomic Physics with the
Goddard High Resolution Spectrograph on the Hubble Space Telescope. IV.
Relative Oscillator
Strengths for Singly-ionized Nickel," Ap. J. 498, 256 (1998). (PDF)
- J. Zsargó, S.R. Federman, and J.A. Cardelli, "Atomic Physics with the
Goddard High Resolution Spectrograph on the Hubble Space Telescope. III. Oscillator
Strengths for Neutral Carbon," Ap. J. 484, 820 (1997). (PDF)
-
S.R. Federman, and J.A. Cardelli, "Atomic Physics with the
Goddard High Resolution Spectrograph on the Hubble Space Telescope. I. Oscillator
Strengths for Neutral Sulfur," Ap. J. 452, 269 (1995). (PDF)
- D.J. Beideck, R.M. Schectman, S.R. Federman, and D.G. Ellis, "Oscillator
Strengths of Selected Resonance Transitions in Neutral Sulfur," Ap. J.
428, 393 (1994). (PDF)
- R.M. Schectman, S.R. Federman, D.J. Beideck, and D.G. Ellis, "Accurate
Oscillator Strengths for Interstellar Ultraviolet Lines of Cl I,"
Ap. J. 406, 735 (1993). (PDF)
- S.R. Federman, D.J. Beideck, R.M. Schectman, and D.G. York, "Accurate
Oscillator Strengths for Ultraviolet Lines of Ar I:
Implications for Interstellar Material," Ap. J. 401, 367 (1992). (PDF)