Mapping the U.S. Scientific Future in VLBI

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Mapping the U.S. Scientific Future in VLBI

• http//www.nrao.edu/VLBIfuture
• VLBIfuture_at_nrao.edu
• ftp.aoc.nrao.edu/pub/VLBIfuture

VLBI Future Committee Shep Doeleman (Haystack
Obs.) Dave Hough (Trinity College) Shri
Kulkarni (Caltech) Colin Lonsdale (Haystack
Obs.) co-chair Alan Marscher (Boston Univ.)
Chris O'Dea (STScI) Greg Taylor (NRAO)
co-chair David Wilner (Harvard-Smithsonian
CfA) Joan Wrobel (NRAO)
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Very Long Baseline Array (VLBA) Dedicated in 1993

• Frequencies ranging from 330 MHz to 86 GHz
• Angular resolution to 100 microarcseconds at
  highest frequency

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Very Long Baseline Interferometry

• Radio interferometry with elements (antennas)
  separated by hundreds to thousands of
  kilometers.
• Cant be connected-element interferometry
• Each antenna has its own frequency and time
  reference
• Data and time stamps recorded on magnetic tape
  (600 GBy)
• Tapes brought together and correlated at a
  central site
• VLBI technique has been around for 30 years
• VLBA is culmination of project to provide VLBI
  capabilities in a more easy-to-use, more
  flexible, always available telescope.

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Free-free absorption in 1946708
Peck Taylor (2001) Spectral index map from
1.3/5 GHz VLBI observations free-free optical
depth tff T-3/2 ne2n-2 d Ne 3 x 1022
cm-2 ionization 10
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EVLA and New Mexico Array

• NMA proposal being reviewed by AUI
• EVLA can provide correlator upgrade for VLBA

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resolution at 5 GHz 10 1
0.1 0.01 0.001
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Mechanisms for High Brightness Radio Emission

• Synchrotron / gyrosynchrotron emission from
  electrons in magnetic fields
• quasars, extragalactic radio jets and lobes
• x-ray binaries (Sco X-1)
• flare stars (AD Leo)
• colliding winds (WR stars)
• SNe
• GRBs
• Maser emission from molecules
• star forming regions
• circumstellar shells in late-type stars
• supernova remnants

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VLA Light Curves (Berger et al 2003, submitted)
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Resolving the Afterglow
4th Epoch May 19 VLBAEBGBTY27 Beam is 0.67
x 0.24 mas Jet component at 0.28 /- 0.05
mas Not consistent with standard
model prediction of 0.12 mas expansion average
expansion velocity of 19c
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HI absorption in 1946708Peck Taylor
(2001)Global VLBIobservationscoret
0.2FWHM 350 km/sNH 3 x 1023 cm-2for Tspin
8000 KM 108 Msun
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• Astrometry Example
• Pulsar Proper Motions
• parallax ok out to 10 kpc

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SiO Masers and Dust Condensation Zone
Photosphere
A few stellar radii
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TX Cam Masers around an evolved star
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SN 1993J
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Discussion Questions

1. In what areas of research are you currently
   active? What types of data do you use, or are
   relevant to your research?
2. Do you currently use VLBI in your research? If
   so, how, and if not, why not?
3. Do you now, or have you in the past, used the
   VLBI results of others to enhance or motivate
   your work? Please elaborate.
4. This request for input was accompanied by a
   summary of present and future VLBI technical
   capabilities. Were you aware, in terms relevant
   to your research, of the capabilities and
   limitations of the VLBI technique before? Might
   it make a difference to you?
5. Also accompanying this request for input was a
   brief account of the multiple ways in which
   present-day VLBI is being used to address
   astronomical and astrophysical issues. Were you
   aware of these ways? Does the versatility of the
   technique pique your interest? If not, what
   about in 5 or 10 years based on the projected
   capabilities of VLBI?

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6. Is lack of funding (e.g. graduate student
support) a significant impediment to including
VLBI observations in your own research
program? 7. In general, if you wanted to get
VLBI data and results, would you make VLBI
observations yourself, or would you pursue a
collaboration? Why? 8. What is your perception
of the accessibility of the VLBI technique? 9.
Based on your view of the future of your field,
and the new instruments and capabilities expected
in coming years, do you see potential synergies
developing with VLBI where none exist
today? 10. Please share any additional insights
you may have on the state and future of VLBI in
the U.S.