Sky conditions at OAGH

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Sky Brightness

Table 1. Typical Sky Brightness at OAGH (mag/sq. arcsec)
Date	B	V	R	I	Instrument	Observer
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	A. Carramiñana+
May 1994	21.50	20.50	20.00	18.70	LFOSC	A. Buzzoni

Atmospheric Extinction

Table 2. Typical Extinction coefficients at OAGH (mag/airmass)
Date	U	B	V	R	I	Instrument	Observer
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	A. Carramiñana+
May 1994		0.215	0.094	0.069	0.099	LFOSC	A. Buzzoni
Average	0.44	0.20	0.11	0.07	0.05

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

The rsulting 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 forest fires!) 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 is given in the last column of Table 2.

 
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Table 3: Extinction Curve for OAGH (Priliminary)
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  lambda (A) 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
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Last Updated: 05Jun2000 by Divakara Mayya