Synthetic Star Forming Region HRDs

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This page contains synthetic Hertzsprung-Russell Diagrams (HRDs) for a simulated Star Forming Region, assuming different scenarios and timescales for the history of star formation. These simulations were described in detail in the paper

``The Stellar Composition of the Star Formation Region CMa R1: I. Results from new photometric and spectroscopic classifications'' by V.S. Shevchenko, O.V. Ezhkova, M.A. Ibrahimov, M.E. van den Ancker & H.R.E. Tjin A Djie, MNRAS 310, 210-222 (1999). <abstract> <reprint>

In the paper we only presented the best fits to the HRD of the CMa R1 Star Forming Region. Here we show the full time evolution in the HRD for each of the considered star formation scenarios in the form of an animated sequence.

Scenario I: Instantaneous star formation

Download movie (1.90 MB)

Scenario II: Constant rate of star formation during a time interval delta t

delta t = 0.1 Myr

Download movie (1.95 MB) delta t = 1.0 Myr

Download movie (2.07 MB) delta t = 10 Myr

Download movie (2.50 MB)

Scenario III: Linearly increasing rate of star formation during a time interval delta t

delta t = 0.1 Myr

Download movie (1.94 MB) delta t = 1.0 Myr

Download movie (2.03 MB) delta t = 10 Myr

Download movie (2.39 MB)

Scenario IV: Linearly decreasing rate of star formation during a time interval delta t

delta t = 0.1 Myr

Download movie (1.98 MB)

delta t = 1.0 Myr

Download movie (2.04 MB)

delta t = 10 Myr

Download movie (2.37 MB)

How were these movies generated?

The simulation itself was done by the C program clusthrd.c. This program first generates a cluster of 5000 stars with main-sequence masses between 0.15 and 100 M_o following the Miller & Scalo (1979, ApJS 41, 513) Initial Mass Function (for T₀ = 1.2 × 10¹⁰ yr) and initial ages following one of the above star formation scenario's.

For each time at which we want to compute a HRD, we then ``evolve'' (i.e. compute log T_eff and log L/L_o) all of these stars using the pre-main sequence evolutionary tracks for z=0.02 by Bernasconi (1996, A&AS 120, 57) for intermediate-mass (M >/= 2 M_o) stars, those by D'Antona & Mazzitelli (1994, ApJS 90, 467) for low-mass (M < 2 M_o) stars and the evolutionary tracks by Schaller et al. (1992, A&AS 96, 269) to follow the post-main sequence evolution of massive stars. Stars which have an age younger than a star of that mass at the birthline in the Bernasconi evolutionary tracks or have reached the end of their post-main sequence track are omitted from the resulting HRD.

For each time point in the final animation, the program clusthrd generates an output file hrd_xxx.dat, with xxx=100, 101, 102, etc., with the HRD data and a plot file hrd_xxx.wip for use with the (superb) wip plotting package. After clusthrd is done, I then use a unix shell script wip2yuv (wip2yuv hrd_*.wip) to first use wip to create a gif picture with the HRD, then use ImageMagick's convert program to convert this gif to a ppm file, and then use the program ppmtoyuvsplit from the netpbm package to split this ppm into its Y, U and V components which are the basis of the mpeg format (I haven't found a program yet which can convert a gif directly into splitted YUV format). Finally, I run the mpeg compression program mpeg with the command line mpeg -PF -a 100 -b 699 -h 424 -v 340 -s hrd.mpeg hrd_ (with 100 the first frame number and 699 the last) to create the movie in mpeg format.

The clusthrd program, together with its input files with the evolutionary tracks and birthline and the wip2yuv script are available for downloading in the gzipped tar file clusthrd.tar.gz.

mvandena@eso.org