Input star catalog
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Show content only (no menu, header)Input star catalog1. Motivation and GoalsTo be habitable, a planet must receive from its host star a flux that is approximately equivalent to the flux received by Earth. When observed in reflected light, the apparent brightness of potentially habitable planets is therefore mostly a function of its distance (to the observer) and mostly independent of the host star brightness. Direct imaging of potentially habitable planet is therefore only possible around nearby stars (typically within 20pc for a ground-based ELT or a medium-sized space telescope). Direct detection of exoplanets is also constrained by contrast detection limits and inner working angle. While contrast limits tend to favor late-type main sequence stars, the inner working angle limit favors detection of habitable planets around early-type main sequence stars for which the habitable zone is further out from the star.Input star catalogs for direct imaging of potentially habitable exoplanets have been previously created for space missions concepts aimed at detection and characterization of Earth-like planets around F-G-K type main sequence stars. The Hipparcos catalog is usually adopted for these mission concepts, as it offers good completeness for F-G-K type stars within the approximately 20pc radius within which space-based telescopes can have the sensitivity to detect and characterize habitable planets. The superior angular resolution offered by ground-based extremely large telescopes (ELTs) brings potentially habitable planets around nearby M-type stars and white dwarfs within reach. For these types of targets, the Hipparcos catalog is incomplete, and other catalogs should be included as well. 2. Input catalogsIn order to cover a wide range of spectral types, several catalogs are used to construct the input star catalog for this study:
3. Combining the catalogsThe six catalogs (SUPERBLINK, CNS3, 2MASS, HIPPARCOS, HIPPARCOS doubles, RECONS) are merged and their content combined according to priority rules, producing a list of 6042 stars within 30pc. While the resulting catalog is complete for early-type stars, only the nearest late type stars are included.The steps and rules to combine the catalogs are:
4. Bolometric LuminosityFor the purpose of this study, the bolometric luminosity of each star needs to be computed. A multi-band photometry (U to L) model for main sequence stars, compiled by Eric Mamajek, is used as a template against which every star is compared. This model is used to fill in the missing data for each star and estimate its bolometric luminosity. The C source code reads the catalogs and does this matching, producing an output target list containing 138155 targets, with the following format.4.1. Computing expected colors for a given stellar effective temperatureThe main challenge in computing bolometric luminosity is for sources for which brightness has only been measured in a few bands. The measurements are fitted to the multi-band photometry model described above, assuming stars belong to the main sequence. This is done using two functions. The first function, named SimulMS_colors, produces, for a given effective temperature Teff, the expected U-B, B-V, V-I, V-K, J-H and H-K colors by interpolating the multi-band photometry data table maintained by Eric Mamajek.
int SimulMS_colors(float Teff)
{
long i0, i1;
float ifrac;
i1 = 1;
while(stfarray_Teff[i1]>Teff)
{
i1++;
if(i1==67)
{
printf("ERROR in SimulMS_colors\n");
exit(0);
}
}
i0 = i1-1;
ifrac = (Teff-stfarray_Teff[i0])/(stfarray_Teff[i1]-stfarray_Teff[i0]);
simulBCv = (1.0-ifrac)*stfarray_BCv[i0] + ifrac*stfarray_BCv[i1];
simulx = (1.0-ifrac)*stfarray_x[i0] + ifrac*stfarray_x[i1];
simulUB = (1.0-ifrac)*stfarray_UB[i0] + ifrac*stfarray_UB[i1];
simulBV = (1.0-ifrac)*stfarray_BV[i0] + ifrac*stfarray_BV[i1];
simulVI = (1.0-ifrac)*stfarray_VI[i0] + ifrac*stfarray_VI[i1];
simulVK = (1.0-ifrac)*stfarray_VK[i0] + ifrac*stfarray_VK[i1];
simulJH = (1.0-ifrac)*stfarray_JH[i0] + ifrac*stfarray_JH[i1];
simulHK = (1.0-ifrac)*stfarray_HK[i0] + ifrac*stfarray_HK[i1];
simulMsun = (1.0-ifrac)*stfarray_Msun[i0] + ifrac*stfarray_Msun[i1];
return(0);
}
The function also computes the V band Bolometric correction , which allows absolute V band magnitudes to be converted to bolometric luminosities. 4.2. Solving for effective temperatureThe effective temperature is obtained by fitting measured colors to the model described above. When a color is not measured (B-V for example), the associated error bar (variable errBV) is set to a very high value so that this color is effectively excluded from the fit. The function Teff_solve() performs the fit and returns the estimated effective temperature.
float Teff_solve()
{
float Teff, Teffopt;
float val, valbest;
float tmp;
FILE *fp;
fp = fopen("TeffFit.txt","w");
Teffopt = 2700.0;
valbest = 1.0e12;
for(Teff=2700.0; Teff<30000.0;Teff*=1.01)
{
val = 0.0;
SimulMS_colors(Teff, 0);
tmp = (valx-simulx)/errx;
val += tmp*tmp;
tmp = (valUB-simulUB)/errUB;
val += tmp*tmp;
tmp = (valBV-simulBV)/errBV;
val += tmp*tmp;
tmp = (valVI-simulVI)/errVI;
val += tmp*tmp;
tmp = (valVK-simulVK)/errVK;
val += tmp*tmp;
tmp = (valJH-simulJH)/errJH;
val += tmp*tmp;
tmp = (valHK-simulHK)/errHK;
val += tmp*tmp;
tmp = (valTeff-Teff)/errTeff;
val += tmp*tmp;
if (val
4.3. Bolometric LuminosityThe star's bolometric luminosity (variable star[k].Blum) is either directly loaded from catalogs if available, or computed. If computed, it is derived from the apparent V-band magnitude of the star, its distance, and the bolometric correction estimated by the SimulMS_colors() function.The following code shows how it is computed if no estimate is available (the statement "if(star[k].Blum < 0.0)" returns TRUE if no estimate is available, as the variable is initialized to -100 at the beginning of the code). Mbol = star[k].MV + simulBCv - 0.076; if(star[k].Blum < 0.0) star[k].Blum = pow(2.51188643,-(Mbol-4.83)); 5. Combined catalog descriptionNote that O and B stars include white dwarfs, as the classification is made entirely based upon effective temperature.Total number of stars:
6. Estimating detection signal-to-noise ratioThe telescope and coronagraph parameters are then used to compute detection sensitivity (quantified by SNR) for each target. The output file, named ResultSNR.txt, follows the following format .
Angular separation vs reflected light contrast for Earths (1x Earth diameter), assuming each star in the sample has such a planet. Stars are colored according to their effective temperature (Log(Teff), colorbar on the right), and the size of each circle encodes the distance to the system (small distance = large circle) [png] Gnuplot command: set terminal png size 600,400 x000000 set out "Earth_sep_contrast.png" set title "Exo-Earths within 20pc" set logscale x set palette rgbformulae 10,34,4 set cbrange [3.4:3.9] set xlabel "Angular Separation (arcsec)" set ylabel "log Contrast" plot [0.004:2][-12:-6] "./StarList_20pc.txt" u 20:(log10($21)):(9.0/$4):(log10($17)) with points pt 6 ps variable lw 2.5 lt palette notitle 3D viewing tool (under development)If your browser supports WebGL and your computer has a GPU, you can use the 3-D viewing tool for the catalog and estimate detection SNR under the simple assumptions considered by the tool: 3D viewing toolPage content last updated: 27/06/2023 06:35:52 HST html file generated 27/06/2023 06:34:38 HST |