MIRLIN Photometry Issues

2001 Mar 16: Actively under construction

The IRTF TAC has been very generous awarding me time to carry out a program to establish a new network of mid-infrared standard stars. After a painfully slow start due to a string of bad weather, the project is finally moving along, and I intend to post preliminary results here as I reduce the data.

Extinction Findings

Atmospheric extinction in the mid-infrared is maddening - at 11 µm, the atmosphere is almost completely transparent, while at wavelengths > 17 µm, it's like extremely variable soup. The CSO has given Mauna Kea an extremely valuable tool with their 225 GHz optical depth monitor. A quick look at their Tau Now (Brown Cow) entry allows one to immediately gauge whether its worth attempting 20 µm observations or not. The rule of thumb as I have found it is as follows:

Tau above 0.4: go home
0.2 to 0.4: 10 µm window only
0.14 to 0.2: 18 µm if you are desperate
0.07 to 0.14: good for 18 µm, 20-25 µm okay for brighter sources
0.04 to 0.07: excellent for all wavelengths
less than 0.04: park the filter wheel at 24.5 µm, tie the telescope operator to his chair, crank up the stereo, and attempt to image every known object in the sky!

Here is my first attempt to quantify this. I hope to eventually be able to say, "If the 225 GHz tau is X, then the extinction coefficient at Y µm is Z." We'll see how it pans out.

Filter	(Units)	N	N0	N1	N2	N3	N4	N5	Q-short	Q1	Q3	Q5
Wavelength	(µm)	10.79	7.91	8.81	9.69	10.27	11.70	12.49	17.90	17.93	20.83	24.48
Passband	(µm)	5.66	0.76	0.87	0.93	1.01	1.11	1.16	2.00	0.45	1.65	0.76

2000 Jun 09 (tau = 0.071)	(mag/airmass)	---	0.181	0.042	0.144	0.058	0.015	0.028	0.218	0.178	0.257	0.336

Standard Stars

The results reported here are very preliminary, but they should show what I'm up to. Zero points, in particular, still require work; for example, Vega (HR 7001) should be roughly 0.00 at all wavelengths, but setting it to -0.07 allowed alpha Boo and beta Peg to better agree with other published values. So, I still have a bit of work to do ...

Filter	(Units)	N	N0	N1	N2	N3	N4	N5	Q-short	Q1	Q3	Q5
Wavelength	(µm)	10.79	7.91	8.81	9.69	10.27	11.70	12.49	17.90	17.93	20.83	24.48
Passband	(µm)	5.66	0.76	0.87	0.93	1.01	1.11	1.16	2.00	0.45	1.65	0.76

HR 5013	---	---	2.19	2.18	2.07	2.15	2.07	2.16	2.03	2.08	2.27	---
		---	± 0.02	± 0.02	± 0.02	± 0.01	± 0.05	± 0.07	± 0.08	± 0.33	± 0.23	---
HR 5340	alpha Boo	---	-3.14	-3.13	-3.21	-3.16	-3.20	-3.20	-3.17	-3.22	-3.14	-3.16
		---	± 0.03	± 0.01	± 0.01	± 0.02	± 0.01	± 0.02	± 0.03	± 0.02	± 0.03	± 0.02
HR 5429	rho Boo	---	0.49	0.48	0.41	0.40	0.50	0.50	0.66	0.54	0.57	0.46
		---	---	---	---	---	---	---	---	---	---	---
HR 6136	---	---	1.88	1.88	1.78	1.81	1.79	1.80	2.10	2.09	1.96	---
		---	± 0.08	± 0.03	± 0.01	± 0.01	± 0.07	± 0.04	± 0.05	± 0.39	± 0.11	---
HR 6388	---	---	2.03	1.97	1.98	1.98	1.90	1.83	1.97	1.79	2.14	---
		---	---	---	---	---	---	---	---	---	---	---
HR 7001	alpha Lyr	---	-0.07	-0.07	-0.07	-0.07	-0.07	-0.07	-0.07	-0.07	-0.07	-0.07
		---	---	---	---	---	---	---	---	---	---	---
HR 7064	---	---	1.96	1.94	1.97	1.88	1.81	1.89	2.06	2.20	1.84	3.81
		---	---	---	---	---	---	---	---	---	---	---
HR 7633	---	---	1.21	1.14	1.09	1.09	1.05	0.98	1.21	1.10	1.20	0.76
		---	---	---	---	---	---	---	---	---	---	---
HR 8032	33 Vul	---	1.94	1.86	1.84	1.90	1.87	1.97	1.84	2.52	1.61	1.31
		---	---	---	---	---	---	---	---	---	---	---
HR 8775	beta Peg	---	-2.39	-2.42	-2.52	-2.49	-2.56	-2.55	-2.53	-2.58	-2.51	-2.52
		---	± 0.02	± 0.00	± 0.01	± 0.00	± 0.00	± 0.00	± 0.01	± 0.00	± 0.01	± 0.01
HR 8876	10 And	---	2.13	2.11	2.12	2.07	1.96	1.97	2.18	2.23	2.14	---
		---	---	---	---	---	---	---	---	---	---	---
HR 8905	ups Peg	---	2.89	2.90	2.84	2.83	3.00	2.80	3.14	---	---	---
		---	---	---	---	---	---	---	---	---	---	---

For questions about this page please contact:

Dr. Michael Ressler (Michael.E.Ressler@jpl.nasa.gov)