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Preparing for MOS observations with the GTC

The pandemic of Covid-19 has obviously affected our observing runs also. ESO is (still) totally shut down while GTC after some off period it seems that it is under some limited operation.

Our accepted observing program with GTC includes Mulit-Object Spectroscopic observations with the OSIRIS instrument. For this we need to prepare masks, i.e. metal plates on which a number of slits is cut to allow the light of specific targets to pass and acquire their spectrum. In order to optimize the positioning of those slits (and make sure that they are placed on the correct coordinates) we have asked for pre-imaging, e.g. the acquisition of short exposures of the FOVs we have requested (for all our targets). With these and the appropriate software (Mask Designer) it becomes easy to create the masks.

Some weeks ago we actually received (quite unexpectedly, given the pandemic status) a couple of images. That allowed us to prepare the corresponding masks (after resolving all technical difficulties and questions of course). An example of these masks is shown below for the galaxy IC 10. When creating the mask we have to avoid slits that result in overlapping spectra (because we will end up with useless data). That’s why we need to prioritize our targets and select the best combination which will allow for the maximum non-colliding number of targets to be observed, respecting all constraints imposed by the program and the instrument involved. Although mask designing with modern software tools can become easy it is still a time-consuming step that needs caution and accuracy.

Mask for multi-slit spectroscopic observations with OSIRIS GTC - Target galaxy IC 10

The image shows the mask designed for the galaxy IC 10. The small white line are the slits with the corresponding spectra visible as vertical thick green lines. Smaller lines correspond to fiducial stars, i.e. stars that help to the alignment of the mask. The yellow box corresponds to the physical limits of the maks. The background image is a short exposure of IC 10 in the r band.

So, the masks have been prepared, verified, constructed, … and now we wait for the real spectroscopic observations to be obtained! Fingers crossed!

note: the current article has been written originally for the ASSESS group.


WhereIsM13 and .jar files

WhereIsM13 is a great 3d visualization application of deep sky objects! You can see where these objects lie in our Galaxy along with their physical properties.

There are different download options according to the operating system.
For linux users download the .zip version which includes a .jar file that can be run by double clicking (well, not in my case…although I changed the properties so as to be executable). If not, then you can easilly run it by typing:

$ java -jar /path/to/file.jar

(there is no need for the file to be executable!).

William Parsons – first direct observation of spirals

William Parsons, was the first to notice spirals in a galaxy. His first scetch was the M51 (Whirlpool Galaxy) in 1845.

W Parsons' M51

More on William Parsons:
> Wikipedia
> A list of photos & discoveries
> Drawings

Useful astronomical numbers

Just some useful numbers and units to remember and to have an easy access to!
[last updated: 29 Dec 2011]

>> Distance

1 AU = 150 x 106 km

1 pc = 3.09 × 1013 km = 206260 AU = 3.26 ly

1 ly = 9.4 x 1012 km = 64 x 103 = 0.31 pc

>> Sun

L = 3.86 x 1026 W = 3.86 x 1033 erg / s

MV,☉ = Mbol,☉ = 4.8

M = 2 x 1030 kg

R = 6.96 x 105 km

V☉,relative = 30 km/s

T = 5780 K

RSun-GC = 8 kpc

tgalactic orbit = 250 x 106 yr

Vgalactic rotation = 200 km/s

solar wind’s energy ~ 10-7 L (on average)

solar wind’s density (in the vicinity of Earth) ~ 5 particles / cm3

solar wind’s velocity (in the vicinity of Earth) ~ 400 km / s

mass loss ~ 10-14 M / yr

>> Earth

MEarth = 5.974 x 1024 kg

REarth = 6371 km

ρEarth = 5.5 g/cm3

>> Milky Way / Galaxy

bulgeradius ~ 5 kpc

diskradius ~ 15 kpc

haloradius > 75 kpc (perhaps 100 kpc)

dust ± 300 pc from disk level

stars ± 1000 pc from disk level

MMW = -20.5 ( 25 mag more than MSun, 1010 times that of Sun)

>> Ionization potential

for H = 13.6 eV

for He = 24.6 eV (one electron) + 54.4 eV (both electrons)

>> Hydrogen atom

R = 1 Å

>> Extinction

Sun’s neighbourhood: ~ 1 mag/kpc

towards GC: ~ 21 mag/kpc – 1 optical photon per 1012 reaches us, while 1 out of 10 in IR

>> magnitude difference: 5 mags = 100 times in flux [m1-m2=-2.5 log10(f1/f2)]