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Mission Overview

Low Resolution Stellar Library (LOWLIB)


Primary Investigator: Guy Worthey

HLSP AuthorsGuy Worthey, Tathagata Pal, Islam Khan

Released: 2023-04-17

Updated: 2023-04-17

Primary Reference(s): Pal et al. 2023

DOI: 10.17909/kmdt-pw63

Citations: See ADS Statistics

Read Me

Source Data:



Stellar distribution of the Next generation stellar library (NGSL)

Library stars are plotted in log Teff, log g space. The previously published stars from HST proposals GO 9088, GO 9786, and GO 10222 (plusses; Koleva & Vazdekis 2012, A&A, 538, 143), and the GO 13776 stars (circles) are split by metallicity, metal-poor (MP): [Fe/H] < -1 (red) or metal-rich (MR): [Fe/H] > -1 (blue). An approximate Eddington stability line and spectral type boundaries are included in the plot as visual guides.

Duplicate spectra of HD145675

Observations of K0 dwarf HD 145675 from two different epochs are overplotted, along with their average. The second of the two is labeled GJ 614. These are fully corrected spectra. The comparison gives an idea of the excellent reproducibility of spectra over time. The existence of two observations, in this case, allowed the elimination of lingering bad pixels in the UV region, but other than that, the reproducibility is excellent.


"Stellar libraries" are collections of stellar spectra. Such libraries find use in population synthesis studies, stellar parameter estimation, exposure time calculators, mission planning, and education.

This HLSP contains 513 stellar spectra in FITS files. The spectra are flux calibrated, dereddened, and shifted to zero velocity. Observed with three low resolution gratings from the HST Space Telescope Imaging Spectrograph(STIS) and then merged into one continuous spectrum, these spectra cover roughly 0.2 < λ < 1 μm at λ/Δλ about 1000. This "HST Low Resolution Stellar Library" extends and supersedes NGSL, the "Next Generation Stellar Library," and comes as a companion to the Hot Star Library (Khan & Worthey 2018, A&A, 615, 115).

Data Products

The metadata file has the following naming convention:


All spectra files have the following naming convention:




  • <target> is the target name, such as "hd011964"
  • <prodType> is either "spect" or "preview"
  • <ext> is either "fits" or "png"


Data file types:


The metadata file of the spectral library


The merged, continuous spectra of three low-resolution STIS gratings, which are fluxed, dereddened, and shifted to zero velocity 

The preview image of each spectrum


Catalog File

The data extension (first extension) of the _metadata.csv file contains literature Teff, log g, [Fe/H], dust extinction (AV), K0 scattered light count rate, and other metadata such as star names and standard photometry. Note that B and V are as observed (not dereddened), but M_V_0 is dereddened. The " Av Src" column is for V-band extinction AV: 1 - Koleva & Vazdekis (2012, A&A, 538, A143), 2 - the HLSP team's derivation based on comparison with synthetic templates, or 3 - Drimmel et al (2003, A&A, 409, 205).

The description of the columns in the catalog file

Column name Unit Description
Simbad name - Simbad identifier
MAST file - MAST filename
Teff (K) K Effective temperature
log g


Surface gravity
[Fe/H] [Sun] Metalicity
B (mag) mag

Apparent B band Vega magnitude

V (mag) mag Apparent V band Vega magnitude
Plx (mas) mas Simbad parallax
M_V_0 mag

(MV)0 , Absolute V band Vega magnitude

dSlit (pix) pix

Slit off-center correction

Vr (km/s) km/s Radial velocity
K_0 (ADU/s) ADU/s

Scattered light count rate at 2000A

Av mag V -band Extinction
Av Src - Source reference of extinction
Mg2800 (mag) mag

Mg II 2800 index

Halpha (mag) mag

Hα index

Hbeta (mag) mag Hβ index
Note - Note about the object

Spectral files

The data extension (first extension) of the _spect.fits files are multi-extension FITS files. Each HDU description is the following. Casual users should choose extension 4 wavelength and fully corrected flux.

FITS Extension HDU Type Description
HDU 1 Primary HDU

Contains no data. The header contains information about basic stellar parameters.



A binary table extension with columns for wavelength (in Angstroms), uncorrected flux, scattered light corrected flux, scattered light & slit off-center corrected flux, and scattered light, slit off-center & dust corrected (fully corrected) flux (fluxes are in erg/s/cm2/Angstrom). Flux errors are also included as separate columns.


Count rate:

A binary table extension with columns for wavelength (in Angstroms), uncorrected count rate, scattered light corrected count rate, scattered light & slit off-center corrected count rate, and scattered light, slit off-center & dust corrected (fully corrected) count rate. Uncertainties are also included as separate columns.


Flux (Log Wavelength Scale):

This binary table extension contains the same information as HDU 2, but rebinned such that the wavelengths are spaced on a uniform log scale with log Delta lambda = 0.0002.


Count Rate (Log Wavelength Scale):

This binary table extension contains the same information as the HDU 3, but rebinned such that the wavelengths are spaced on a uniform log scale with log Δλ = 0.0002.


Data Access

Spectra are available in the MAST Portal (web-based, cross-mission search interface) and Astroquery (Python package to search for and download files from Python scripts you write), and via the direct download table below. Set the Provenance Name filter to LOWLIB in the Portal Advanced Search to find all or individual spectra. Each observation in the Portal contains a single source's spectra. The spectra can also be retrieved programmatically by using the astroquery—mast module. See the code example below for retrieving and downloading all files. The metadata and spectra files can also be accessed via direct download below.

from astroquery.mast import Observations
all_obs = Observations.query_criteria(provenance_name="lowlib")
data_products = Observations.get_product_list(all_obs)


  • A web-based interface for cross-mission searches of data at MAST or the Virtual Observatory
  • Search for and retrieve LOWLIB data products programmatically.

Direct download

Files Size Description
hlsp_lowlib_hst_stis_all_g230lb-g430l-g750l_v1.0_metadata.csv 448 KB Metadata file

177 MB


165 MB Preview images



Please remember to cite the appropriate paper(s) below and the DOI if you use these data in a published work. 

Note: These HLSP data products are licensed for use under CC BY 4.0.