34 research outputs found
Harmonizing the RR Lyrae and Clump Distance Scales - Stretching the Short Distance Scale to Intermediate Ranges?
I explore the consequences of making the RR Lyrae and clump giant distance
scales consistent in the solar neighborhood, Galactic bulge and Large
Magellanic Cloud (LMC). I employ two major assumptions: 1) that the absolute
magnitude - metallicity, M_V(RR) - [Fe/H], relation for RR Lyrae stars is
universal, and 2) that absolute I-magnitudes of clump giants, M_I(RC), in
Baade's Window are known (e.g., can be inferred from the local Hipparcos-based
calibration or theoretical modeling). A comparison between the solar
neighborhood and Baade's Window sets M_V(RR) at [Fe/H] = -1.6 in the range
(0.59 +/- 0.05, 0.70 +/- 0.05), somewhat brighter than the statistical parallax
solution. More luminous RR Lyrae stars imply younger ages of globular cluster,
which would be in better agreement with the conclusions from the currently
favored stellar evolution and cosmological models. A comparison between Baade's
Window and the LMC sets the M_I^{LMC}(RC) in the range (-0.33 +/- 0.09, -0.53
+/- 0.09). The distance modulus to the LMC, mu^{LMC}, is between 18.24 +/- 0.08
and 18.44 +/- 0.07. Unlike M_I^{LMC}(RC), this range in mu^{LMC} does NOT
depend on the adopted value of the dereddened LMC clump magnitude,
I_0^{LMC}(RC). I argue that the currently available information is insufficient
to select the correct distance scale with high confidence.Comment: version accepted to MNRAS, added discussion about the dependence of
the results on theoretical assumptions and observational input, stressed that
the derived range of the LMC distance modulus between 18.24 and 18.44 is
insensitive to the controversial dereddened I-magnitude of the LMC clump
giant
The Distance to the Large Magellanic Cloud
I demonstrate that the two unexpected results in the local Universe:
anomalous intrinsic (V-I)_0 colors of RR Lyrae stars and clump giants in the
Galactic center, and very short distances to Magellanic Clouds inferred from
clump giants, can be at least partially resolved with a modified coefficient of
selective extinction A_V/E(V-I). With this modification, I find a new
clump-giant distance modulus to the Large Magellanic Cloud, mu_{LMC} = 18.27
+/- 0.07, which is 0.09 larger than the Udalski (1998b) result. When distance
estimates from the red clump, RR Lyrae stars and the eclipsing binary HV2274
are combined, one obtains mu_{LMC} = 18.31 +/- 0.04 (internal).Comment: less detailed and more review-style version of ApJ Letter (528, L9),
to be published in the ASP Conference Series Vol. 203, 1999: ``The Impact of
Large Scale Surveys on Pulsating Star Research'', L. Szabados and D. Kurtz,
ed
A Test for the Origin of Quasar Redshifts
It is commonly accepted that quasar redshifts have a cosmological character
and that most of the quasars are at Gigaparsec distances. However, there are
some cases where several quasars with completely different redshifts and a
nearby active galaxy are aligned in a certain way or occupy a very small patch
on the sky, which is claimed by some authors to be unlikely to happen by
chance. Is there a small subset of quasars with non-cosmological redshifts? For
quasars apparently associated with galaxies, we consider two scenarios for the
origin of their redshift: 1. a standard, cosmological scenario, 2. a
velocity-induced Doppler shift of a nearby object's spectrum (local, ejection
scenario). We argue for a simple astrometric test which can distinguish between
these two sources of quasar redshifts by constraining their proper motions.
We give the predictions for the maximum possible proper motions of a quasar
for the cosmological and local scenarios of the origin of their redshifts. We
apply these theoretical results to the Bukhmastova (2001) catalog, which
contains more than 8000 close QSO-galaxy associations. In the standard
interpretation of quasar redshifts, their typical proper motions are a fraction
of micro arc-second, and beyond the reach of planned astrometric missions like
GAIA and SIM. On the other hand, the quasars ejected from local AGNs at
velocities close to the speed of light would have proper motions 5-6 orders of
magnitude larger, which would easily be measurable with future astrometric
missions. The distributions of proper motions for the cosmological and local
scenarios are very well separated. Moreover, the division corresponds nicely to
the expected accuracy from GAIA and SIM.Comment: results unchanged, minor additions, 10 pages, 6 figures, 1 table,
accepted to MNRA
Total to Selective Extinction Ratios and Visual Extinctions from Ultraviolet Data
We present determinations of the total to selective extinction ratio R_V and
visual extinction A_V values for Milky Way stars using ultraviolet color
excesses. We extend the analysis of Gnacinski and Sikorski (1999) by using
non-equal weights derived from observational errors. We present a detailed
discussion of various statistical errors. In addition, we estimate the level of
systematic errors by considering different normalization of the extinction
curve adopted by Wegner (2002). Our catalog of 782 R_V and A_V values and their
errors is available in the electronic form on the World Wide Web.Comment: 20 pages, 7 figures, submitted to Acta Astronomic
Correcting Parameters of Events Based on the Entropy of Microlensing Ensemble
We entertain the idea that robust theoretical expectations can become a tool
in removing hidden observational or data-reduction biases. We illustrate this
approach for a specific problem associated with gravitational microlensing.
Using the fact that a group is more than just a collection of individuals, we
derive formulae for correcting the distribution of the dimensionless impact
parameters of events, u_min. We refer to the case when undetected biases in the
u_min distribution can be alleviated by multiplication of impact parameters of
all events by a common constant factor. We show that in this case the general
maximum likelihood problem of solving an infinite number of equations reduces
to two constraints, and we find an analytic solution. Under the above
assumptions, this solution represents a state in which the ``entropy'' of a
microlensing ensemble is at its maximum, that is, the distribution of u_min
resembles a specific, theoretically expected, box-like distribution to the
highest possible extent. We also show that this technique does not allow one to
correct the parameters of individual events on the event by event basis
independently from each other.Comment: 16 pages, version accepted by ApJ, results unchanged, additional
discussion regarding conditions suitable for application of the presented
metho
An introduction to economic analysis in medicine - the basics of methodology and chosen terms. Examples of results of evaluation in nuclear medicine
This article overviews the basic terms and methodology approaches in economic analysis in medicine: cost-benefit analysis, cost-effectiveness analysis, cost-utility analysis and costminimisation analysis. Particular emphasis is put on nuclear medicine economic evaluation, e.g. FDG - PET studies, sestamibi
breast cancer imaging and radioiodine therapy of hyperthyroidism
The Zero Point of Extinction Toward Baade's Window
We measure the zero point of the Stanek (1996) extinction map by comparing
the observed (V-K) colors of 206 K giant stars with their intrinsic (V-K)_0
colors as derived from their H\beta indices. We find that the zero point of the
Stanek map should be changed by \Delta A_V = -0.10 +/- 0.06 mag, obtaining as a
bonus a three-fold reduction of the previous statistical error. The most direct
way to test for systematic errors in this determination would be to conduct a
parallel measurement based on the (V-K) colors of RR Lyraes (type ab).Comment: 10 pages, 1 figur