.. _p5-nebular-extinction:

P05: Nebular Extinction
=======================

Observing Goals:
^^^^^^^^^^^^^^^^

In this project you will observe a nebula or edge-on galaxy and try to determine the extinction due to dust in the nebula or galaxy. 
Useful Background and References:

    * Osterbrock & Ferland 2005
    * :ref:`r03-narrow-lines`

Observation Planning:
^^^^^^^^^^^^^^^^^^^^^

    * Observation Time

        * You will be observing HALF a night.

    * Target Selection

        * Depending on your group, you should select either an edge-on spiral galaxy or a nebula.
        * Your target should be as high as possible in the sky (i.e. lowest airmass) for the duration of your observations.
        * Your target should fit nicely within the frame of the CCD.

    * Observations

        * Take images of your nebula in the :math:`{\rm H\beta}`, :math:`{\rm V}`, :math:`{\rm H\alpha}`, and :math:`{\rm R}` filters. 
        * Note that the :math:`{\rm H\beta} filter images will need to be much longer (total exposure time) than the other images.
        * We strongly suggest that you take all of your images, including the calibration images (flat fields and bias frames), with the imaging CCD in :math:`{\rm 3 \times 3}` binning mode. (This reduces the resolution of your images but greatly improves the signal-to-noise.)

Data Analysis:
^^^^^^^^^^^^^^^

    * Data Reduction Basic Steps

        * Visit the page :ref:`data-reduction`
        * Register and combine your images for each filter.

    * Further for this project

        * Create an :math:`{\rm H_{\alpha}/H_{\beta}}` image.
        * To make it even more precise, you might want to first subtract the R-band image from the :math:`{\rm H\alpha}` image and the V-band image from the :math:`{\rm H\beta}` image.

    * Further Analysis for this project
        * Refer to this page for the flux knowledge :ref:`r03-narrow-lines`
        * Compare the values of the :math:`{\rm H_{\alpha}/H_{\beta}}` ratio across the image. In a fully calibrated image the ratio will be 2.74 in fully calibrated flux units in the case of emission from 10000K nebula with pure :math:`{\rm H}` and :math:`{\rm He}` ("case B recombination"; see Osterbrock & Ferland 2005). 
        * Any variation from this number means that there is extinction by dust in the nebula.

Results: 
^^^^^^^^

Can you answer these questions with your work?

    * Q1: Is there any variation in the ratio :math:`{\rm H_{\alpha}/H_{\beta}}`?
    * Q2: If so, why? If not, why not?

Presenting your results:
^^^^^^^^^^^^^^^^^^^^^^^^

   - :ref:`a1-poster`
   - :ref:`a2-talk`