13 research outputs found
A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
We present UBVRI photometry obtained from Mosaic images of M31 and M33 using
the KPNO 4-m telescope. The survey covers 2.2 sq degrees of M31, and 0.8 sq
degrees of M33, chosen so as to include all of the regions currently active in
forming massive stars. The catalog contains 371,781 and 146,622 stars in M31
and M33, respectively, where every star has a counterpart (at least) in B, V,
and R. We compare our photometry to previous studies. We provide cross
references to the stars confirmed as members by spectroscopy, and compare the
location of these to the complete set in color-magnitude diagrams. While
follow-up spectroscopy is needed for many projects, we demonstrate the success
of our photometry in being able to distinguish M31/M33 members from foreground
Galactic stars. We also present the results of newly obtained spectroscopy,
which identifies 34 newly confirmed members, including B-A supergiants, the
earliest O star known in M31, and two new Luminous Blue Variable candidates
whose spectra are similar to that of P Cygni.Comment: Accepted by the Astronomical Journal. A version with higher
resolution figures can be found at:
http://www.lowell.edu/users/massey/M3133.pdf.g
A Survey of Local Group Galaxies Currently Forming Stars: III. A Search for Luminous Blue Variables and Other H-alpha Emission-Lined Stars
We describe a search for H-alpha emission-lined stars in M31, M33, and seven
dwarfs in or near the Local Group (IC 10, NGC 6822, WLM, Sextans B, Sextans A,
Pegasus and the Phoenix dwarf) using interference filter imaging with the KPNO
and CTIO 4-m telescope and Mosaic cameras. The survey is aimed primarily at
identifying new Luminous Blue Variables (LBVs) from their spectroscopic
similarity to known LBVs, avoiding the bias towards photometric variability,
which may require centuries to manifest itself if LBVs go through long
quiescent periods. Followup spectroscopy with WIYN confirms that our survey
detected a wealth of stars whose spectra are similar to the known LBVs. We
"classify" the spectra of known LBVs, and compare these to the spectra of the
new LBV candidates. We demonstrate spectacular spectral variability for several
of the new LBV candidates, such as AM2, previously classified as a Wolf-Rayet
star, which now shows FeI, FeII and Balmer emission lines but neither the NIII
4634,42 nor HeII 4686 emission that it did in 1982. Profound spectral changes
are also noted for other suspected and known LBVs. Several of the LBV
candidates also show >0.5 mag changes in V over the past 10-20 years. The
number of known or suspected LBVs is now 24 in M31, 37 in M33, 1 in NGC 6822,
and 3 in IC 10. We estimate that the total number of LBVs in M31 and M33 may be
several hundred, in contrast to the 8 known historically through large-scale
photometric variability. This has significant implications for the time scale
of the LBV phase. We also identify a few new WRs and peculiar emission-lined
objects.Comment: Accepted by the Astronomical Journal. Version with higher quality
figures may be downloaded from http://www.lowell.edu/users/massey/has.pdf.g
A Survey of Local Group Galaxies Currently Forming Stars: II. UBVRI Photometry of Stars in Seven Dwarfs and a Comparison of the Entire Sample
We have obtained UBVRI images with the Kitt Peak and Cerro Tololo 4-m
telescopes and Mosaic cameras of seven dwarfs in (or near) the Local Group, all
of which have known evidence of recent star formation: IC10, NGC 6822, WLM,
Sextans B, Sextans A, Pegasus,and Phoenix. We construct color-magnitude
diagrams (CMDs) of these systems, as well as neighboring regions that can be
used to evaluate the degree of foreground contamination by stars in the Milky
Way. Inter-comparison of these CMDs with those of M31, M33, the LMC, and the
SMC permits us to determine improved reddening values for a typical OB star
found within these galaxies. All of the CMDs reveal a strong or modest number
of blue supergiants. All but Pegasus and Phoenix also show the clear presence
of red supergiants in the CMD, although IC10 appears to be deficient in these
objects given its large WR population. The bright stars of intermediate color
in the CMD are badly contaminated by foreground stars (30-100%), and
considerable spectroscopy is needed before statistics on the yellow supergiants
in these systems will be known. This study is intended to serve both as the
impetus and "finding charts" for further space-based imaging, and for many
spectroscopic programs at large aperture.Comment: Added Erratum. Revised versions of Tables 12 and 13 can be found at
http://www.lowell.edu/users/massey/Table12Revised.txt and
http://www.lowell.edu/users/massey/Table13Revised.tx
Univariate and multivariate strategies for the rheological tests evaluation: Influence of additives in composite materials
Filler formulations are complex systems, characterized by a high number of components with different nature, as resins, extenders, additives. One of the main properties of a two-component epoxy filler used for yacht application is the rheology. Thus, rheological additives are studied in both components after different times from the production. Rheological analysis produces a very large amount of information so statistical methods are useful to elaborate the data. In this study, a univariate approach (ANOVA) and a multivariate data processing, namely, principal component analysis after low-level data fusion are carried out. It is shown that the multivariate approach provides the maximum useful information on the system. No differences are highlighted in the rheological behavior for the epoxy component, by using different additives while, for the polyamide component, the best rheological additive among the tested is the one that has a polyamide nature, being a polar system as itself