Two Amusing Papers f/ ArXiv:astro-ph

First a little background, there is a roughly elliptical
region of stellar overdensity in Canis Major at l=240, b=-7
( Martin, Ibata, et al, 2004 MNRAS, 384, 12 ). The nature
of this overdensity is under discussion, the discovery paper
suggested that it was the core of an accreting satelite,
the Canis Major dwarph spheroidal galaxy.

In arXiv:astro-ph/0405526, _Probing the Canis Major stellar
over-density as due to the Galactic warp_ Momany, Zaggia, et al
fired a shot across the bow.

This did not go un-noticed, in arXiv:astro-ph/0407391, _Why the
Canis Major overdensity is not due to the Warp: analysis of
its radial profile and velocities_ Martin, Ibata, et al
defended their original conclusions by, among other reasons,
positing a better model of the Warp.

Who is right? Stay tuned, I'm sure that we will see several
papers about this, hopefully we will see a clear example of
professionals working towards a consensus. One thing to note
is that the authors are always polite and stick to the data
and even discuss the weakness' of their own positions. I wouldn't
be surprised if they shared data or even if workers from
"opposing sides" co-authored future papers.

Certain posters ( not just on this list ) could take a hint
from this.

For your convenience I'll post the abstracts:

=============
Probing the Canis Major stellar over-density as due to
the Galactic warp

Authors: Y. Momany (1), S. Zaggia (2), P. Bonifacio (2),
G. Piotto (1), F. De Angeli (1), L. R. Bedin (1),
G. Carraro (1)
((1) Dip. di Astr., Univ. Padova,
(2) INAF - Oss. Astr. Trieste)
Comments: Accepted for publication in A&A Letters, 4 pages

Proper-motion, star counts and photometric catalog simulations
are used to explain the detected stellar over-density in the region
of Canis Major (CMa), claimed to be the core of a disrupted dwarf
galaxy (Martin et al. 2004, Bellazzini et al. 2003), as due to the
Galactic warp and flare in the external disk. We compare the kinematics
of CMa M-giant selected sample with surrounding Galactic disk stars
in the UCAC2 catalog and find no peculiar proper motion signatu
CMa stars mimic thick disk kinematics. Moreover, when taking into
account the Galactic warp and flare of the disk, 2MASS star count
profiles reproduce the CMa stellar over-density. This star count
analysis is confirmed by direct comparison with synthetic color-
magnitude diagrams simulated with the Besancon models
(Robin et al. 2003) that include the warp and flare of the disk.
The presented evidence casts doubt on the identification of the
CMa over-density as the core of a disrupted Milky Way satellite.
This however does not make clear the origin of over-densities
responsible for the ring structure in the anticenter direction of
the Galactic halo (Newberg et al. 2002; Yanny et al. 2003;
Zaggia et al. 2004, in preparation).

=============
Why the Canis Major overdensity is not due to the Warp: analysis
of its radial profile and velocities

Authors: N. F. Martin, R. A. Ibata, B. C. Conn, G. F. Lewis,
M. Bellazzini, M. J. Irwin, A. W. McConnachie
Comments: 5 pages, 4 figures, submitted to MNRAS

In response to criticism by Momany et al. (2004), that the
recently-identified Canis Major (CMa) overdensity could be simply
explained by the Galactic warp, we present proof of the existence
of a stellar population in the direction of CMa that cannot be
explained by known Galactic components. By analyzing the radial
distribution of counts of M-giant stars in this direction, we show
that the Momany et al. (2004) warp model overestimates the number
of stars in the Northern hemisphere, hence hiding the CMa feature
in the South. The use of a better model of the warp has little
influence on the morphology of the overdensity and clearly displays
an excess of stars grouped at a distance of 7.2\pm 0.3 kpc. To lend
further support to the existence of a population that does not belong
to the Galactic disc, we present radial velocities of M-giant stars
in the centre of the CMa structure that were obtained with the 2dF
spectrograph at the AAT. The extra population shows a radial velocity
of v_r=109\pm5 km/s, which is significantly higher than the typical
velocity of the disc at the distance of CMa. This population also has
a low dispersion (11\pm4 km/s). The Canis Major overdensity is therefore
highly unlikely to be due to the Galactic warp. This could reflect the
possibility that the Warp has a peculiar structure at this location,
that we are observing an outer spiral arm, or that this overdensity
is the remnant of an accreted dwarf galaxy. This leads to questions
on what part of CMa was previously identified as the Warp and how to
possibly disentangle the two structures.
=============

Dark skies,

tom

--
We have discovered a therapy ( NOT a cure )
for the common cold. Play tuba for an hour.