Instruments’ Guide

Instruments’ Guide
The Mont-Mégantic Observatory is captured in this photograph against the backdrop of the starry night sky, with the Milky Way, our galaxy, visible in the background. Credit: Harun Mehmedinovic.


An astronomer at the Observatoire du Mont-Mégantic works on the PESTO instrument.

Instrument Features

Field of View at l’OMM 7.95′ x 7.95′
Plate Scale at l’OMM 0.466″/pixel
Nüvü Detector 1024 x 1024 pixels, EMCCD
Min Read-time in Standard Mode 1070 milli-seconds
TimeStamp GPS

Available filters

There are 6 filter positions available. The filters available are: g’, r’, i’ z’ and Halpha, produced by ASTRODON (photometric sloan filters).
Additional filters can be added quickly during missions.
Filter size is 1.25″ (3.175cm).

Filtre λ nm Δλ nm
g’ 401-550
r’ 562-695
i’ 695-844
z’ 826-920
656.3 3

Observing modes

Image Quality at Zenith (FWHM)


All articles using PESTO data must include the following statement:

“Based on observations obtained with PESTO at the Mont-Mégantic Observatory, funded by the Université de Montréal, Université Laval, the Natural Sciences and Engineering Research Council of Canada (NSERC), the Fond québécois de la recherche sur la Nature et les technologies (FQRNT) and the Canada Economic Development program.”

Les publications PESTO

Rappaport, S. et al., 2017,Monthly Notices of the Royal Astronomical Society, Volume 471, Issue 1, p.948-961 WD 1202-024: the shortest-period pre-cataclysmic variable

Questions? Feel free to contact us!

David Lafrenière :


Basic instrument characteristics

Field of view (OMM) 30’x30′
Pixel scale (OMM) 0.89″/pixel
Detector 2048 x 2048 pixels, Hawaii II
Minimum integration time 1.35 s
Integration time is always a multiple of 1.35 s
Overhead per exposure 5 s
Overhead per dither (<30″) ~5-10 s
Overhead for slews of more than a few arcminutes ~30-45 s
Median Full Width at Half-Maximum (FWHM) at the OMM 2.0″
Readout noise ~10 electrons
Linearity imit ~30 000 ADU per coadd
Gain ~2.5 e-/ADU
Transmission 30-35%

Available filters

CPAPIR two filter wheels can only hold up to 10 filters. Filters will be changed depending on the semester’s requests.

Filter λ Δλ
J 1.25 μm 0.16 μm
Paβ 1.2814 μm 0.012 μm
CH4 1.57 μm 0.05 μm
H 1.65 μm 0.30 μm
CONT2 2.033 μm 0.025 μm
HeI 2.062 μm 0.015 μm
CIV 2.081 μm 0.02 μm
H2 2.122 μm 0.023 μm
Ks 2.15 μm 0.30 μm
Brackett γ 2.165 μm 0.02 μm
HeII 2.192 μm 0.04 μm
CONT1 2.255 μm 0.10 μm

Getting started with your CPAPIR proposals

Here is the relevant information the you should include in your CPAPIR proposal :

If you proposal includes more than one target, you should prioritize them.

The required exposure time may be estimated from the values listed in the table below. As a rule-of-thumb, the limiting magnitude increases as 1.25×log(T) and decreases with the seeing as 2.5×log(FWHM). The 5σ limiting magnitude for observations taken under a 2.5″ seeing and a total exposure time of 2 hours in J band will therefore be


This estimate has a 0.3 mag accuracy in J and 0.5-1.0 mag in H and Ks.

Filter 5 σ sensitivity
J 19.4
H 17.5
Ks, outside temperature > 10C 16.5
Ks, outside temperature < -5C 18.0

Length of individual exposures

Please follow the exposure times suggested bellow. If you wish to use exposure times that differ significantly from the ones below, please contact us before submitting your proposal. It is not possible to read subarrays of CPAPIR’s detector at a high cadence, this feature is only available on Hawaii-II RG arrays.

J band : 1 co-addition of 20 s
H band : 2 co-additions of 10 s
Ks band : 3 co-additions of 8 s
narrow bands : 1 co-addition of 60 s

As a general rule, the per co-addition median of your images should not be above 10 000 ADUs as you would loose significantly in dynamic range. If the background is above 30 000 ADUs per coadd, your dataset will probably be useless!

Image quality constraints

Observing conditions at the Observatoire du Mont-Mégantic are typical of a continental site with a 2.0″ median seeing measured with CPAPIR (including the instrumental PSF). If the angular resolution is important to meet your science goals, you may add as a constraint that the observation be done only under a seeing better than the 2.0″. Of course, this constraint will decrease the likelihood that your observations be completed. The histogram of full width at half maximum values for the whole dataset of CPAPIR observations taken at the OMM is available below. The estimated FWHM without instrumental degradation assumes an instrumental contribution of 1.2″.

Timing constraints

Queue mode observations allow time-constrained observations, but you must remember that a good fraction of the nights are lost to clouds. Certain types of time-constrained observations are nevertheless well suited for this mode, such as exoplanet transit followups that have many timing windows through the semester. If you which to submit such a proposal, please submit an ascii table of the observing windows (UT time) with your proposal.

For other types of timing constraints, please contact us before submitting your proposal.

Dither pattern

You must specify the dither pattern for your observations. Your project most likely will fall within one of these four categories:

Photometry of a single source

If you wish to get the best photometric accuracy for a single point source, the dither pattern will only be within a 30″x30″ box. This strategy minimizes the effects of flat field illumination and may reach a photometric accuracy of a few milimagnitudes for bright targets.

Stellar field without extended source

If you observe a stellar field without any extended (>1′) object, we will use a 5’×5′ dither pattern. This pattern will give a uniform sensitivity through the field and good sky subtraction.

Extended object smaller than 15′

If your field has extended objects (more than 1′ but less than 15′), we will use a dither pattern that moves the target in the four corners of the field. This strategy gives a good sky subtraction while always keeping the target within the field.

Extended object larger than 15′

If your target takes more than half the field of CPAPIR, sky frames off the field will have to be taken. In that case, the required exposure time will be doubled, and you must double the requested exposure time for your proposal.

Data reduction

The Université de Montréal LAE’s team developped a data reduction pipeline for the analysis of CPAPIR datasets. In addition to your raw data, you will receive fully reduced data with astrometric and photometric calibration.

Photometric calibration

With CPAPIR’s wide field of view, there will always be numerous 2MASS stars in every frame (50 at galactic poles, 15 000 toward the galactic center). The catalog can be used to derive a reasonably precise photometric calibration to the percent level of all datasets. Observations can be obtained under light clouds without having to observe a flux standard. This calibration is included in the CPAPIR data reduction pipeline. Note that the CPAPIR’s J filter is significantly narrower than the 2MASS J filter and avoids the telluric absorption beyond 1.34 μm. CPAPIR uses a ‘MaunaKea’ (Jmko) J filter. For L and T dwarfs, this introduces a photometric bias relative to the 2MASS photometry, please read this paper for more details on this matter.

Archival data

The CPAPIR data is archived, from 2005 up to today, to the Canadian Astronomy Data Centre. The data is corrected for astromtry (_SCI). You will find reduced and combined data as well (_SCIRED). Please note that the data reduction pipeline is not optimized for extended objects. Therefore, you will need to use a more appropriate method developped for galaxy or HII region on the _SCI data.


All paper using CPAPIR data must include the following note in the “Acknowledgement” section :

“Based on observations obtained with CPAPIR at the Observatoire du mont Mégantic, funded by the Université de Montréal, Université Laval, the Natural Sciences and Engineering Research Council of Canada (NSERC), the Fond québécois de la recherche sur la Nature et les technologies (FQRNT) and the Canada Economic Development program.”

CPAPIR publications

You need a few ideas for your CPAPIR proposal? Here are the publications that made use of CPAPIR data :

Artigau et al., 2010, Proc SPIE, 7737, 63 Queue observing at the Observatoire du Mont-Mégantic 1.6-m telescope
Walter et al., 2009, AIPC, 1094, 568W Very Low Mass Objects in Orion OB1a and b
Radigan et al., 2009, ApJ, 698, 405 Discovery of the Widest Very Low Mass Field Binary
Faherty et al., 2009, AJ, 137, 1 The Brown Dwarf Kinematics Project I. Proper Motions and Tangential Velocities for a Large Sample of Late-Type M, L, and T Dwarfs
Cushing et al., 2009, ApJ, 696, 986 2MASS J06164006–6407194: THE FIRST OUTER HALO L SUBDWARF
Boudreault & Bailer-Jones, 2009, AIPC,1094, 904B A Constraint on brown dwarf formation via ejection: radial variation of the stellar and substellar mass function of the young open cluster IC 2391
Artigau et al., 2009, ApJ, 701,1534 Photometric Variability of the T2.5 Brown Dwarf SIMP J013656.5+093347: Evidence for Evolving Weather Patterns
Artigau et al., 2009, AIPC, 1094, 493A SIMP: A Near-Infrared Proper Motion Survey
Chene & St-Louis, 2008, IAUS, 250, 139C The First Determination of the Rotation Rates of Wolf-Rayet Stars
Artigau et al., 2007, ApJ,659L,49A Discovery of the Widest Very Low Mass Binary
Artigau et al., 2006, ApJ, 651L, 57A Discovery of the Brightest T Dwarf in the Northern Hemisphere
Demers et al., 2006, A&A, 456, 905D Carbon stars in the outer spheroid of NGC 6822
… we forgot your paper? Please send us an email!

Questions? Feel free to contact us!

Étienne Artigau :