Photometry

In article , Wolfi
writes:
For near-infrared filters, things get more complicated with the
inclusion of air transmission accounting e.g. for water vapor and the
response functions are shaped quite considerably by the atmosphere.

Which filters do you mean? Most of the practical bands are not too
bad.

However, also in the optical regime the atmosphere has important
contribution (with telluric lines, oxygen molecules etc...). I always
though that such effects are corrected in the published photometry on
night-by-night basis, so that's why filter transmission curves only
are enough to generate synthetic optical magnitudes.

If you want accurate synthetic magnitudes, you have to take the
various bands into account. Yes, published photometry is corrected
at some level on a night-by-night basis but generally to a "standard
star system," which has some average value of atmospheric
transmission, not 100%.

But in the infrared case, the atmospheric contribution must is
included in the filter transmissions published in literature.

Which ones did you have in mind? Most filter curves I've seen don't
include atmospheric transmission. I don't see how it would be
possible, given the differences between sites. Photometry at, say,
Mauna Kea is a lot different than at, say, Kitt Peak.

Is published infrared photometry actually not corrected on
night-by-night basis to eliminate the atmospheric contribution?

There are in practice two corrections. Published photometry is
corrected night-by-night for local extinction. This is usually taken
to be color-independent, though that isn't necessarily the case. In
addition, there are (much smaller) corrections for the different
photometric systems at different observatories. These arise from
slight variations in transmission of filters and other optics as well
as differences in altitude and water vapor content. The latter
corrections are often neglected; they are important only for very
precise work on very red stars or stars with unusual spectral
properties.

If you have specific questions, feel free to contact me by email.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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