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INAOE | Astrophysics | Observatories | OAGH | The Observatory | Sky conditions: brightness, extinction and seeing
 

Observation Conditions at Mount Mariquita

The sky at the Cananea site

Preliminary data available on sky brightness, extinction and seeing.

 Sky Brightness

 

Table 1. Typical Sky Brightness at OAGH (mag/sq. arcsec)
Date B V R I Instrument Observer Ref.
4 Feb 2000 21.66 20.85 20.44 18.96 CamDir D. Mayya
May 1998 21.90 20.94 20.49 18.77 LFOSC A. Carramiñana+
Jan 1997 21.80 20.00 19.80 18.50 LFOSC E. Carrasco et al. [1]
May 1994 21.50 20.50 20.00 18.70 LFOSC A. Buzzoni [1,2]

We note that Buzzoni 1994 measures were taken towards the West, the direction opposite to the city of Cananea, while the 1997 measures were made in the direction of Cananea. Light pollution can account for the 0.7 and 0.5 mag/arcsec excess brightness observed in B and V respectively, with no significant excess in R and I.

 


Atmospheric Extinction

 

Table 2. Typical Extinction coefficients at OAGH (mag/airmass)
Date U B V R I Instrument Observer Ref
23 Oct 1999 0.440 0.200 0.110 0.110 0.070 CCD at 16-inch A. Carramiñana+
May 1998   0.347 0.217 0.132 0.128 LFOSC A. Carramiñana+
30 Jan 1998   0.185 0.120 0.050 0.040 LFOSC D. Mayya+I.Puerari
Jan 1997   0.243 0.139 0.090 0.064 LFOSC E. Carrasco et al. [1]
May 1994   0.215 0.094 0.069 0.099 LFOSC A. Buzzoni [1,2]
Average 0.44 0.20 0.11 0.07 0.05    

 

  • Except for the night in May 1998, of conditions anomalous, the rest are fitted by a curve involving 2 terms:
    1. Rayleigh scattering: lambda-4
    2. Aerosol scattering: lambda-0.8
    The exact equation with the fitted coefficients is written on the plot and the corresponding extinction values are tabulated in Table 3 below.
  •  

    The resulting curve is plotted in red. The night of May 1998 fitted separately and the resulting curve is shown by light blue (this night was affected by smoke from serious forest fires all over Mexico and USA!)

    Considering the proximity of KPNO (longitude = 111:36.0 deg, latitude = 31:57.8 deg, altitude = 2120 m) to OAGH (longitude = 110:23.0 deg, latitude = 31:03.2 deg, altitude = 2480 m), it is of interest to compare the extinction curves of the two observatories. Dashed line in the above figure represents the typical curve for KPNO (taken from IRAF database). It should be remembered that the extinction curve of KPNO is from narrow band photometry, where as our curve is based on UBVRI bands. Mean values of extinction at OAGH (excluding the smoky night) at the UBVRI bands are given in the last column of Table 2.

    Table 3: Extinction Curve for OAGH
    (Preliminary!)
    lambda (Å) K(lam)
    3000 0.689
    3200 0.550
    3400 0.447
    3600 0.371
    3800 0.312
    4000 0.266
    4200 0.230
    4400 0.201
    4600 0.178
    4800 0.159
    5000 0.143
    5200 0.130
    5400 0.119
    5600 0.109
    5800 0.101
    6000 0.094
    6200 0.088
    6400 0.083
    6600 0.079
    6800 0.074
    7000 0.071
    7200 0.068
    7400 0.065
    7600 0.062
    7800 0.060
    8000 0.057
    8200 0.055
    8400 0.054
    8600 0.052
    8800 0.050
    9000 0.049
    9200 0.048
    9400 0.046
    9600 0.045
    9800 0.044
    10000 0.043


    Seeing

     

  • Measurements made with the DIMM seeing monitor starting in April 1998. Preliminary analysis of the periods with more data available gives:

    Table 4: Seeing measurements
    Statistic February-March 1999 October-December 1999
    1st cuartile 0.851 0.708
    Median 0.993 0.828
    3rt cuartile 1.177 0.979

  • Because of the set-up used for the seeing monitor all values are in fact upper limits. The difference between the early and late 1999 data might be due to the different set-ups, rather than the atmosphere.
    Work in progress...
  •  


    References:

    1. Carrasco, B.E., Carramiñana, A., Sánchez-Sesma, F.J. & Lermo, F.J., 1998,
      in Preserving the Astronomical Windows,
      ASP Conf Ser 139, 141

    2. Buzzoni, A., 1994,
      INAOE Technical Report 169.

    Last Update:
    26-11-2008 a las 14:07 by

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