scholarly journals Synthetic photometry of globular clusters: Uncertainties on synthetic colors

2018 ◽  
Vol 616 ◽  
pp. A164 ◽  
Author(s):  
F. Martins

Context. Synthetic photometry is a great tool for studying globular clusters, especially for understanding the nature of their multiple populations. Aims. Our goal is to quantify the errors on synthetic photometry that are caused by uncertainties on stellar and observational/calibration parameters. These errors can be taken into account when building synthetic color-magnitude diagrams (CMDs) that are to be compared to observed CMDs. Methods. We have computed atmosphere models and synthetic spectra for two stars, Pollux and Procyon, that have stellar parameters typical of turn-off and bottom red giant branch stars in globular clusters. We then varied the effective temperature, surface gravity, microturbulence, the carbon, nitrogen, and oxygen abundances, and [Fe/H]. We quantified the effect on synthetic photometry in the following filters: Johnson UBVRI and HST F275W, F336W, F410M, F438W, F555W, F606W, and F814W. We also estimated the effects of extinction, atmospheric correction, and of the Vega reference spectrum on the resulting photometry. In addition, we tested the ability of our models to reproduce the observed spectral energy distribution and observed photometry of the two stars. Results. We show that variations are generally stronger in blue filters, especially those below 4500 Å. Dispersions on synthetic colors due to uncertainties on stellar parameters vary between less than 0.01 and to 0.04 magnitude, depending on the choice of filters. Uncertainties on the zero points, the extinction law, or the atmospheric correction affect the resulting colors at a level of a few 0.01 magnitudes in a systematic way. The models reproduce the flux-calibrated spectral energy distribution of both stars well. Comparison between synthetic and observed UBVRI photometry shows a variable degree of (dis)agreement. The observed differences indicate that different reduction and calibration processes are performed to obtain respectively observed and synthetic photometry, and they call for publication of all the details of the reduction process to produce synthetic photometry at a 0.01 mag level, which is required to interpret observed CMDs.

2015 ◽  
Vol 456 (1) ◽  
pp. 181-191 ◽  
Author(s):  
Ya. V. Pavlenko ◽  
B. Kaminsky ◽  
M. T. Rushton ◽  
A. Evans ◽  
C. E. Woodward ◽  
...  

2015 ◽  
Vol 12 (S316) ◽  
pp. 320-327
Author(s):  
Santi Cassisi

AbstractRecent spectroscopic and photometric surveys of Galactic Globular Clusters have shown that these stellar systems host distinct sub-populations of stars characterised by peculiar chemical patterns. In the following we wish to address the issue of how these specific chemical patterns affect both the structural and evolutionary properties of stars as well as their spectral energy distribution. The implications of these effects on the photometric appearance of multiple stellar populations in different photometric planes are also briefly discussed.


2011 ◽  
Vol 20 (3) ◽  
Author(s):  
S. Simić ◽  
L. Č. Popović ◽  
P. Jovanović

AbstractHere we consider the influence of microlensing on the spectrum of a lensed object with the angular size 5 μas accepting that the composite emission of this object originates from three different regions arranged around its center. We assume that the lensed object has three concentric regions with a black-body emission; the temperatures of these regions are 10 000 K, 7500 K and 5000 K. We investigate how the integral spectral energy distribution (SED) of such stratified source changes due to microlensing by a group of solarmass stars. We find that the SED and flux ratios in the photometric B, V and R passbands show considerable changes during a microlens event. This indicates that the flux anomaly observed in some lensed quasars may be caused by microlensing of a stratified object.


2017 ◽  
Vol 470 (2) ◽  
pp. 1342-1359 ◽  
Author(s):  
S. K. Andrews ◽  
S. P. Driver ◽  
L. J. M. Davies ◽  
P. R. Kafle ◽  
A. S. G. Robotham ◽  
...  

2007 ◽  
Vol 477 (1) ◽  
pp. 95-104 ◽  
Author(s):  
M. S. Clemens ◽  
O. Vega ◽  
A. Bressan ◽  
G. L. Granato ◽  
L. Silva ◽  
...  

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