Proposal methods

CHARA offers two methods of applying for time. Consortium members may propose through an internal call for proposals. This process is advertised on the CHARA mailing list and coincides with the NOAO proposal deadline.

Non-consortium members may request community access time through the National Optical Astronomy Observatory. We are offering 25 nights of community access time at the CHARA Array in the 2018A observing semester (February - July).  Proposals will be submitted through NOAO and are due on October 2, 2017.  More information about this observing opportunity can be found on the NOAO-CHARA informational page.  Time should be requested in half-night increments, with a minimum allocation of 0.5 nights (about 5 hours).   Observations will be conducted by CHARA consortium staff at Mount Wilson Observatory, however, visitors are encouraged to travel to the Array to participate in the observations. P.I.'s can apply for travel support once the time allocation process is complete.  Consortium members will support data reduction to Optical Interferometry FITS format (OIFITS), although most users find it interesting (and not that difficult) to run the reduction software themselves. Information about the data reduction pipelines can be found on the data reduction and individual instrument pages. Modeling and image reconstruction software may be found in the data analysis section of this website, the Jean-Marie Mariotti Center, and the Exoplanet Science Institute.

CHARA capabilities

The CHARA Array enables scientific exploration in almost all areas of contemporary astronomy. It is particularly suited to stellar astrophysics where it is used to measure the diameters and effective temperatures of stars, the masses and distances in binary systems, and to image spots and flares on stellar surfaces. Other science topics have included measuring the fundamental parameters of  exoplanet host stars, imaging circumstellar disks, and resolving bright transient phenomena like novae.

All objects observed must satisfy all magnitude requirements for acquisition, tracking, and beam combination listed in the table below. At present, CHARA has no off-axis guiding capabilities.  More information about the baselines and beam combiners can be found on the CHARA Facility and Instrumentation pages.

Instrument Availability in 2018A: Following major upgrades, MIRC is currently in shared-risk mode, which means that the instrument team needs to be involved in the data reduction and resulting publications to ensure basic data quality and to allow use of the data for engineering and data validation purposes. There is also a possibility that the observations cannot be carried out this semester.  All other combiners are available in normal observing mode.

ModeTelescopesBandTypical limit Mag=Best performance Mag=At Spectral Resolution R=
Acquisition 2 V-R 10.0 12.0 Broad band
Tilt tracking 2 V-R 10.0 12.0 Broad band
CLASSIC 2 H or K band 7.0 8.5 Broad band
CLIMB 3 H or K band 6.0 7.0 Broad band
VEGA (hi-res) 2 or 3 2 bands of 7nm (separation 30nm) in 480-850nm 4.0 5.0 30000
VEGA (med-res) 2 or 3 2 bands of 35nm (separation 160nm) in 480-850nm 6.5 7.5 6000
MIRC 6 H 4.5 6.0 40
PAVO 2 630-900 nm 7.0 8.0 30
JouFLU 2 K band 4.5 5.0 Broadband

Note: Limiting performance is achieved on point-source targets. For resolved sources, the limiting performance should be scaled lower proportional to the fraction of flux that is correlated (as measured by the fringe visibility amplitude).  Tools referenced below on the Data Analysis pages can be useful for this estimation, and CHARA or NOAO staff can provide guidance.

The 6 CHARA telescopes provide 15 baselines, listed here. Normally a two-telescope combiner can be used with any two telescopes (one baseline), a 3-telescope combiner with any 3 telescopes (3 baselines), etc. The selection of telescopes can be changed during the night, within some limitations, provided it is part of the observing request and plan - please inquire for more specific information.

Time required for an observation

A single interferometric “snapshot” is taken in a calibrator-science-calibrator sequence. This process requires ~30-90 minutes.  The Planning an Observation page contains more information on the observing time required for each instrument.  Each observation may produce between one to several dozen UV points, depending on the instrument.  The number of calibrated observations needed depends on the science objectives:

  • For an angular diameter or limb-darkening strength, several calibrated sets of data on at least one baseline are required.
  • For a binary separation, a minimum of three calibrated observations or observations on at least three baselines are required.
  • Imaging more complex sources requires many calibrated observations on multiple baselines during the night to fill in the sky coverage.

Proposal tools

Please see the Planning an Observation page for guidelines on selecting the beam combiner, telescopes, and calibrators, and for detailed instructions on how to plan observations. Observations may be planned using either Aspro2 developed by JMMC or the chara_plan2 software distributed with the CLASSIC/CLIMB data reduction software.  An example of how to use Aspro2 and chara_plan2 to plan observations is available here.  Interferometric calibrators may be found using SearchCal or getCal.

Steve Ridgway (ridgway (at) noao.edu) is the NOAO point of contact for proposal preparation.  Gail Schaefer (schaefer (at) chara-array.org) is the CHARA Visitor Support Scientist.