Information for Proposers

  1. Instrument Description
  2. Proposal Guidelines and Restrictions
  3. Mailing List
  4. Raw Sensitivity
  5. Observing Modes and Scan Strategy
  6. Pointing and Calibration
  7. Observing Efficiency
  8. Data Archiving
  9. Analysis Software
  10. Revision History
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Instrument Description

Bolocam, a large-format bolometric camera for observations at 1.1 and 2.1 mm, is open to proposals.  The camera will in general be available for only one of these wavelengths in any given semester.  The camera has 115 working pixels with 8 arcmin FOV (approximately circular).  The beam FWHM is 30 arcsec at 1.1 mm and 60 arcsec at 2.1 mm.  At all wavelengths, the pixel spacing (nearest neighbors of hexagonal close-packed array) is 38 arcsec.

wavelength unless otherwise indicated: 1.1 mm

Proposal Guidelines and Restrictions

Proposals that overlap the instrument team's key projects (blank-field surveys at 1.1 mm for dusty extragalactic point sources, blank-field surveys at 2.1 mm for clusters using the Sunyaev-Zeldovich effect, and pointed observations of galaxy clusters for dusty extragalactic point sources and the Sunyaev-Zeldovich effect) will only be considered if in collaboration with or approved by the instrument team.

All other science topics are open to all proposers, though collaboration with the instrument team is strongly encouraged.  While analysis software will be made available publicly via this web site, the lack of funding for support limits the instrument team's availability for providing technical support on the software to those projects with instrument team members involved as collaborators. 

Prospective proposers are encouraged to contact members of the instrument team with questions or to investigate possibilities for collaboration:

Jamie Bock (
Jason Glenn (
Sunil Golwala (
Phil Mauskopf (

Prospective proposers should endeavor to make such contacts or requests well in advance (> 1 month) of proposal deadlines; the instrument team cannot guarantee immediate response to such requests.

Mailing List

As of March, 2004, we have started a mailing list for Bolocam proposers/users who would like to be notified of major web page updates, especially with regard to sensitivity calculations and analysis software.  Please contact href="BolocamSupport.html">the Bolocam support person if you would like to be added to this list.

Raw Sensitivity

Due to the short history of observations with Bolocam, exhaustive sensitivity numbers are not available.  We give below those numbers that are available.

At 1.1 mm:

Observations taken during the early 2003 El Nino give the following per-pixel instantaneous sensitivity percentiles at 1.1 mm:

unchopped mode

25%: 68 mJy √sec
50%: 78 mJy √sec
75%: 92 mJy √sec

chopped mode:
25%: 102 mJy √sec
50%:  112 mJy √sec
75%:  167 mJy √sec

Cumulative distributions are shown here (NOTE: the horizontal axis must be scaled by 3.4!): pdf

The chopped observations took place partially after the end of the El Nino and give more representative sensitivities.  For the purpose of proposals, we suggest the use of the following 1.1 mm sensitivities:
unchopped mode: 100 mJy √sec
chopped mode:     143 mJy √sec

For survey mode, one can calculate a mapping speed from

MS = Npix Ωbeam / sensitivity2

Npix = 115
Ωbeam = 0.32 arcmin2

giving (approximately)
unchopped mode: 13 arcmin2 hr-1 mJy-2
chopped mode:       6 arcmin2 hr-1 mJy-2

The above results are based on an aggressive sky subtraction.  For "blank-field" data, this aggressive subtraction seems to have a noticeable but small effect on source fluxes (~20% currently).  For bright and/or extended sources, such an aggressive sky removal cannot be applied if accurate recovery of flux from bright and/or extended sources is desired.  A much less aggressive sky subtraction preserves such structures but also results in poorer sensitivity.  Therefore, we ask that proposers use the following mapping speeds depending of their type of observation and observing mode:
Observations not taken in survey mode should begin with the above instantaneous sensitivity numbers and then correct for the number of pixels on-source at any given time as discussed below

Regardless of observing mode, proposers should take account of various observing efficiency factors listed below in estimating the amount of time needed for a given observation.

Observing Modes and Scan Strategy

Observations with bolometric cameras require some sort of temporal modulation of the astronomical signal in order to separate such signal from sky noise and instrumental 1/f.  This need is reflected in the available scanning modes.
Important additional notes on scan strategy:
Proposers must mention their intended observing mode(s) so the CSO TAC may judge whether the desired observations are consistent with the constraints imposed by a bolometric camera.

Pointing and Calibration

Pointing observations must be done frequently with Bolocam.  It is strongly suggested that observers use multiple pointing sources near the field to be observed (within 10 to 20 deg), checking pointing once every 2 hours or so, more frequently if near zenith and the field's local coordinates are changing quickly.  The pointing sources should be spread out so that the pointing on the field of interest can be interpolated, not extrapolated, from the grid.  Pointing sources with fluxes of 2 Jy and higher are easiest to use, though lower-flux sources can be used if necessary.  Pointing sources effectively become relative flux calibration observations by dint of doing them frequently, but they must be tied to primary or secondary flux calibrators at some point during your observing.

Absolute flux calibration on a primary or high-quality secondary calibrator should be done once or twice per night, more frequently if observing conditions are highly variable.  Bolocam has continuous monitors of sky loading (the bolometer resistances) that can be used to do a running relative flux calibration correction, but sufficient data must be accumulated to measure check that this relationship maintains its standard form.   In general, your pointing observations will serve this purpose.

A beam map/flux calibration of the full array should be done once every few nights using a primary calibrator such as Mars (Jupiter and Saturn are too bright) or a bright secondary calibrator (Uranus, Neptune, or bright quasars or galactic sources).  Even for short (1-2 night) runs, at least one beam map should be done.

Relative gains of the array elements can be monitored using sky noise.

More information on doing calibration observations is provided on the PreparingForObserving page.

Observing Efficiency

In calculating time requirements, five important observing efficiency factors should be taken into account:
  1. Turnaround Efficiency

    At high scan speeds and for small fields, a significant amount of observing time may be spent in turnarounds.  We have not optimized the turnaround time, but we have found that the standard turnaround time of 10 sec (5 to slow down, 5 to speed up) provides the sensitivities given above.  Shorter turnaround times may be possible.  To be conservative, observers should assume 10 sec turnaround time and all turnaround time is lost.  This contributes an efficiency factor

    etaturn = (l/vscan) / [ (l/vscan) + tturn ]

    where l is the scan length, vscan is the scan speed, and tturn is the turnaround time.

    When in slow raster + chopping mode, the efficiency is greatly increased due to the slow scan speed.

  2. "Sampling" Efficiency

    The Bolocam array does not instantaneously provide full sampling of the sky.  The array has a hexagonal close-packed format, with pixels spaced by 38 arcsec.  The beam FWHM is 30 arcsec at 1.1 mm and 60 arcsec at 2.1 mm, so the effective pixel spacing is 1.3 f lambda and 0.6 f lambda, respectively.  Full sampling requires a rectangular array with 0.5 f lambda pixel spacing, so clearly instantaneous full sampling is not achieved.

    However, the camera can be rotated relative to the scan direction such that full sampling is achieved after one full pass of the array across a line perpendicular to the scan direction.  While the sky is fully sampled in this mode, it is not necessarily uniformly sampled due to the distribution of bad pixels in the array.  When the sampling is not uniform, the noise will vary across the map.  Observers must therefore realize that one pass across the source will not suffice to provide a uniform map!  For most observers, who will make many scans across a field, the scan strategy can be arranged to provide fairly uniform (to better than a few percent) sampling after many scans.  But observers proposing to observe a field smaller than or comparable to the field of view for only a short amount of time should consult the PreparingForObserving page to determine whether they will need to observe a source for longer than expected in order to build up a uniformly sampled map.

  3. "Mapping" Efficiency

    The coverage in any scan mode will decrease at the edges of the map because the entire array does not sweep over the edges of the field defined by the scan strategy.  The field edges defined by the scan strategy correspond to the motion of the center of the array.  If the center of the array scans to a certain point, only half the array has scanned past that point, so the coverage is reduced to approximately 50% of its value at the center of the field.  The coverage will grade down linearly from 100% to 50% over the last FOV/2 = 4' at each edge of the map.  To conservatively estimate this inefficiency, observers should assume that an edge of width FOV/2 = 4' is lost around the edges of the map.

    For example, for a square map of size 30' x 30' (dimensions indicate the path that the telescope boresight follows), the full coverage region will be only 22' x 22', corresponding to a mapping efficiency of only 0.54.  In general, the mapping efficiency is

    etamap = (lx - FOV) (ly - FOV) / lx ly

    where lx and ly are the dimensions in the x and y directions of the scan.  Alt-az rasters over long periods (where field rotation has an effect) will yield uniform coverage only over a circle whose diameter is the smaller of lx - FOV and ly - FOV, corresponding to lower mapping efficiency.  These formulae become inaccurate when lx and/or ly become comparable to the FOV or smaller.

  4. Point-Source Photometry Mode

    Observations of a single object small compared to the FOV,  as opposed to operation in survey mode, can be quite inefficient because only a few pixels are on-source at any time.  For photometry of point sources, effectively only 1 pixel is on-source at any given time and so one should assume the per-pixel instantaneous sensitivities given above rather than the survey-mode mapping speeds.  For distributed sources small compared to the field of view, one must similarly correct, calculating a mapping speed based only on the number of on-source pixels.

  5. Pointing and Calibration

    The time spent on pointing and calibration should be included in calculation of observing time.  Typical pointing and flux calibration observations only require 5 min + slewing time because they only require the center bolometers of the array cross over the source.  Full-array beam maps and flux calibration scans require large amounts of time (30 min in unchopped mode, 60 min to 2 hrs in chopped mode!), but need only be done once every few nights.

Data Archiving

See the DataArchiving page.

Analysis Software

An archive of the Bolocam analysis pipeline (written in IDL) with some example execution scripts will be made available via the AnalysisSoftware page.  Directions for operating the pipeline are provided there also.  A more detailed manual will be available in the future.  The pipeline is installed in the bolocam account on, one of the summit computers, for use during your observing run.

We emphasize that this pipeline is neither foolproof nor fully automated.  While we expect the pipeline to improve with time (and hopefully user contributions!), it is important that proposers realize that bolometer camera data is, unlike any other kind of astronomical data, a nontrivial exercise in timestream signal processing and noise correlation analysis.  Proposers should judge whether the time investment is worth the expected science return.  The instrument team will not be available for on-demand technical support except in collaborative relationships.

Revision History

Questions or comments? Contact the Bolocam support person.