where to find the tables of irreducible character of the sporadic simple groups and their automorphism groups?

Question

I need tables of complex irreducible characters of the sporadic simple groups and their automorphism groups $Aut(G)$ for some calculation. Also I need information about maximal subgroups of $Aut(G)$

Where Can I find them ?

I checked ATLAS but I am not able to find anything useful. I guess I am missing something.

For example Take $G=M_{12}$

http://web.mat.bham.ac.uk/atlas/html/M12.html

The page does not have any information about $Aut(G)$, also I am not able to locate character table(complex irreducible )

Edit

I am reading from Inverse Galois Theory by Gunter Malle. Regarding Why I need these tables, see the attached image. He has done all the calculation by using data from ATLAS.

Edits 2

Why these Character Tables are different ?

Answer 1

Here is some GAP code to compute it, and display it.

gap> M12 := PrimitiveGroup(12,2);
M(12)
gap> A := AutomorphismGroup(M12);
<group with 7 generators>
gap> G := Image(IsomorphismPermGroup(A));
<permutation group of size 190080 with 7 generators>
gap> C := CharacterTable(G);
CharacterTable( <permutation group of size 190080 with 7 generators> )
gap> Display(C);

...

Edit: As Alexander Konovalov has pointed out, you can do this more easily be reading the character table from the library, and for the larger sporadic groups this approach would be much better, because it would take longer to compute them from scratch.

gap> C := CharacterTable("M12.2");
CharacterTable( "M12.2" )

Answer 2

The book "ATLAS of Finite Groups" (which is probably related to the online "ATLAS of Finite Group Representations that you linked to) contains these character tables, including the character table of $M_{12}$:

Answer 3

The online version of the ATLAS you linked to is obsolete. You find a more current version at http://brauer.maths.qmul.ac.uk/Atlas/v3/

Regarding your example of $M_{12}$, the page http://brauer.maths.qmul.ac.uk/Atlas/v3/spor/M12/ lists representations, conjugacy classes and maximal subgroups not only for the group $M_{12}$ itself, but also for the automorphism group and their double covers.