How can I omit downloading default themes in drupal core in make file Is it possible to not download the default themes- e.g. bartik, garland etc, in my make file when I download the drupal core?
No, I do not believe a makefile (assuming you mean Drush Make) can do this.  Deleting the actual theme files is not the best approach, since each time core is updated they will be re-downloaded.

If you want to remove core themes from the Appearance admin section, you can hide them with hook_system_info_alter().

function example_system_info_alter(&amp;$info, $file, $type) {
  if ($type == 'theme' &amp;&amp; $info['name'] == 'Bartik') {
    $info['hidden'] = TRUE;
  }
}