Determine target magnitude for observing proposal

  • Thread starter abgg
  • Start date
  • Tags
    Magnitude
In summary, the target magnitude for an observing proposal refers to the brightness of the object being observed and is typically measured in apparent magnitude. Determining the target magnitude is important for planning and selecting appropriate equipment and exposure times. Several factors, such as distance, size, reflectivity, and atmospheric conditions, can affect the target magnitude. To calculate the target magnitude, information on the object's distance, size, intrinsic brightness, and atmospheric conditions is needed. The target magnitude can change during the course of an observing proposal due to various factors, and it is important to monitor and adjust observations accordingly for accurate data collection.
  • #1
abgg
1
0

Homework Statement


Hi I have some homework that requires me to write an observing profile for a number of targets. The goal is to obtain B and V band images that can be used to measure integrated photometry as well as surface brightness profiles with a spatial resolution of at least 4kpc.

Have been given a number of targets in the form:
Ra; Dec; Total V Mag (Vega); Major axis (arcmin); Peak Surface Brightness (mag/arcsec^2); Morphological type; Redshift

For one of the targets it is Total V mag =13.4, Major axis=2.3, Peak surface brightness=17.5, type: Sb, z=0.001

Can also assume that the galaxies have a flat surface brightness distribution.

Homework Equations

The Attempt at a Solution


I am currently trying to work out the exposure times, I have determined a date range that is suitable and the corresponding airmass at different times. I am using an exposure calculator found at https://www.eso.org/observing/etc/bin/gen/form?INS.NAME=FORS+INS.MODE=imaging but it requires a target magnitude. I am not sure how to work out this value from what is given. I was expecting a value around ~24 as a guess. Aiming for a SNR of at least 10.

Thanks for any advice or pointers you can give.
 
Physics news on Phys.org
  • #2


Hello,

your main goal in this situation is to obtain B and V band images with a spatial resolution of at least 4kpc. To achieve this, you will need to determine the appropriate exposure times for your target.

To do this, you can use the following equations:

1. The exposure time (t) is equal to the signal-to-noise ratio (SNR) squared, divided by the square of the target magnitude (m) times the sky background (B) and the instrument efficiency (e):

t = (SNR)^2 / (m^2 * B * e)

2. The sky background (B) can be calculated using the following equation:

B = B0 * 10^(0.4 * (m0 - m))

where B0 is the sky background at a reference magnitude (m0), and m is the target magnitude.

3. The instrument efficiency (e) can be determined from the exposure calculator you are using, or from the instrument documentation.

Using these equations, you can calculate the exposure time required to achieve a certain SNR for your target. Keep in mind that the SNR is dependent on the desired level of precision and the noise in the system, so you may need to adjust your exposure time accordingly.

In addition, you can also use the given information about the target's total V magnitude, major axis, and peak surface brightness to estimate the target magnitude. This can be done by assuming a flat surface brightness distribution and using the following equation:

m = V_mag - 2.5 * log10(2 * pi * (major_axis/2)^2 * 10^(0.4 * (peak_surface_brightness - 24.5)))

where V_mag is the total V magnitude, major_axis is the major axis in arcmin, and peak_surface_brightness is the peak surface brightness in mag/arcsec^2.

I hope this helps with your calculations. Good luck!
 

FAQ: Determine target magnitude for observing proposal

What is the target magnitude for an observing proposal?

The target magnitude for an observing proposal refers to the brightness of the object you want to observe. It is typically measured in terms of the apparent magnitude, which is how bright the object appears to an observer on Earth.

Why is determining the target magnitude important for an observing proposal?

Determining the target magnitude is important because it helps you plan and prepare for your observations. It allows you to select the appropriate equipment and exposure times needed to capture the desired data.

What factors affect the target magnitude for an observing proposal?

Several factors can affect the target magnitude for an observing proposal, including the distance of the object from Earth, its size and reflectivity, and its intrinsic brightness. Atmospheric conditions, light pollution, and the sensitivity of your equipment can also impact the target magnitude.

How do I calculate the target magnitude for my observing proposal?

To calculate the target magnitude, you will need to know the distance, size, and intrinsic brightness of the object, as well as the atmospheric conditions and sensitivity of your equipment. You can then use mathematical equations or online calculators to determine the apparent magnitude of the object.

Can the target magnitude change during the course of an observing proposal?

Yes, the target magnitude can change during the course of an observing proposal. This can happen due to a variety of factors, such as changes in the object's position in the sky, variations in its brightness, or changes in atmospheric conditions. It is important to monitor and adjust your observations accordingly to ensure accurate data collection.

Similar threads

Surface brightness profiles: sech^2 fit in mag/arcsec^2 units?
Replies
1
Views
5K
Anomalous Quasar Observations 200k Light Year Jet? And So On.
Replies
11
Views
4K

Hot Threads

Recent Insights

Back
Top