Check TAUVEX Exposure Time Constraints
		Since TAUVEX is moving on a geostationary orbit, the pointing observations are not possible and TAUVEX is always in a scanning mode. The exposure time per scan depends on the celestial declination of the source; for a source at the celestial equator it is 216 seconds. Using our online TAUVEX Exposure Time Calculator (ETC) it is possible to estimate the exposure time per scan for a source at any given declination.

However, exposure time per scan increases with the declination, and at the celestial poles it is possible to observe for 86400 seconds (see the Figure below). Another positive feature is the possibility of repeated scans, thus increasing S/N Ratio.

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		Check TAUVEX Magnitude Constraints
		For a quick estimate of whether a source is observable with TAUVEX, we have presented the tables of the limiting sensitivities for all TAUVEX filters for most types of stars and few representative quasars.

If the proposed source does not fall into those two categories, or some more scientific information is necessary to estimate the observability, we suggest consulting our Online Science Tools library, which includes

		TAUVEX Exposure Time Calculator (ETC)		calculates the exposure time for a given S/N or, alternatively, S/N for a given exposure time
		Stellar Flux Calculator		calculates the flux using Kurucz models for given spectral types
		Coordinate Converter (requires a java enabled browser)		recalibrates the coordinates of the sources (A downloadable version (jar-java archive) and source code are available in the Downloads Area)

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		Check TAUVEX Bright Objects Constraints
		To prolong the life of TAUVEX detectors, it is important to avoid the overexposure to the bright UV sources. The microchannel detectors have a finite reservoir of charge that can be extracted. Exposure to bright sources depletes the charge and will result in rapid decay of the detector sensitivity. Therefore it is of importance that the proposer makes sure the requested target(s) have fluxes that are below the bright limit. The current brightness limit is 20,000 counts per second (cps) per telescope.

Given that many astronomical objects are brighter than this limit, we have adopted at present the following bright objects avoidance policy. It should be noted that it is observer's responsibility to check for any bright inertial target in the field of view that might compromise observations. However, there are special modes for observing targets that are brighter than this limit by a factor of a few. Due to the lower effective area in the narrow-band filters, NBF3 and SF1, the brightness limit for these filters is higher. Observation of such targets is subject to clearance by the TAUVEX Core Group based on detector safety considerations.

1. TAUVEX does not observe near the Sun, the Moon and bright planets (see Planet Table of cps below).
 
The Sun avoidance angle is always 90°.
The current Moon avoidance angle is 5°.
We cannot observe Venus (too close to the Sun).
Jupiter's avoidance angle is 3.5°.
Mars avoidance angle is 2°.
 
Other major planets (Saturn, Neptune, Uranus) are of no danger to TAUVEX. The avoidance angles were calculated using measured TAUVEX PST (see below). We are still in the process of accessing the avoidance of the other Solar System bright objects. At present the TAUVEX Observation Planning tool (TOP) is being created which will estimate the feasibility of observations according to the season and time of the day with Sun, Moon, Jupiter and Mars avoidance. We will also place the ephemerids of bright Solar System objects.

Planet Table of cps for 200 sec exposure time.

2. TAUVEX does not observe very bright UV stars.
 
The brightness limits for all TAUVEX filters are 20,000 cps, which for point sources (assuming flat spectrum) correspond to the following fluxes (in ergs cm^-2s^-1Å^-1):

Some of the early type stars are estimated to have the following limiting brightness magnitudes in V. Stars brighter than those given in the table below cannot be observed by TAUVEX.

Bright Stars (Supergiants) limits in apparent m_V for 200 sec exposure time.

3. Straylight from Nearby Bright Sources

Observations close to a bright source are limited by a straylight. A useful output from the straylight analysis is a set of predicted point source transmission curves. The point-source transmission function (PST) is the inverse of the ratio of the flux density of an off-axis source to the flux density at the telescope focal plane due to light scattered from that source. The PST on the Figure is the measured function for the TAUVEX BBF. Such plots can be used to estimate the straylight contribution from a given source. For example, at 250 nm, Mars (assumed to be a point source when outside the field of view) has a flux density of ~1.8x10^-11 ergs s^-1 cm^-2, which is too high to be observed due to the brightness excess. From the Figure, the BBF (centered at 250 nm) PST at 2° off-axis is 7.0 x 10^-3, so the predicted flux density in the TAUVEX focal plane due to Mars at 2° off-axis is ~1.3x10^-13, which is below the threshhold.  
 

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		Check TAUVEX Orbital Constraints
		Strong observational constraints, like necessity to avoid the Sun at 90° and strictly scanning mode of observation, force restrictions on observing time. At present we accepted the following observational strategy:

Seasonal Observational Strategy

Observable Windows

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		Check Originality of the Proposed Project
		Since for several aspects of UV science with TAUVEX the working groups have been already created, we suggest checking out the Working Groups list to ensure that a planned proposal is new and unique.

We also suggest writing to the respective leaders of the Working Groups for science planning discussion or to TAUVEX team members responsible for the science planning (Margarita Safonova, e-mail: rita@iiap.res.in and/or Rekhesh Mohan, e-mail: reks@iiap.res.in)

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