def open_csv(filename):
    """ Open a light curve file in csv format and extract from it flux time
    series.
    
    Parameters
    ----------
    filename : str
        file name of the ascii file containing the photometry
    
    Returns
    -------
    filename : str
        The filename serves as a unique identifier for the object
    photometry : Astropy table
        Columns are named after the file header and contain time, flux
    """
    photometry = ascii.read(filename, format='csv')
    return filename, photometry
