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SpectroWeb Status June 2012

SpectroWeb Rationale

SpectroWeb was developed to provide the astronomical community with publicly available interactive digital spectral atlases of bright stars for the identification of spectral features used in a wide range of scientific and instrumental applications. The demand for publicly available standard spectral atlases is steadily increasing with the fast improvements in spectral wavelength resolution and the quality by which bright stars of nearly all spectral types are being observed with modern spectrographs. Printed atlases of stellar spectra often only provide a small list of identified features without an assessment of the reliability of the spectral line identifications. Users often have no means of telling whether or not the spectral line identifications are valid, or if they have been revised since publication. On the other hand, many public databases with spectral line information (that can be text queried on-line), are based on theoretical calculations that have not been tested, or are difficult to test against observed stellar spectra. Users often cannot verify if the provided line lists apply to their spectroscopic observations. The spectral line information can contain identifications that do not apply to an observed stellar spectrum because of unknown atmospheric formation conditions or elemental abundance differences with the solar values. Conversely, observed spectral features can often not be identified because the quality of the provided atomic and molecular line data is limited and requires further improvements.

SpectroWeb has been developed to provide users with a means to directly assess the quality of spectral line identifications by comparing high-quality observed spectra of bright stars with state-of-the-art computed spectra through an interactive on-line application. The program currently allows users to select 10 and 25 Å spectral regions of interest from an interactive list of observed wavelengths. The continuum normalized observed and computed spectra are overplotted and marked with spectral line identifications when the central flux of the lines differs by more than two percent from the flux level of the stellar continuum. The user can further enlarge (zoom in) the displayed spectral regions by selecting smaller regions of interest by pressing and releasing the left mouse button. Atomic, molecular, and Earth spectral line identifications in the region of interest can be selected and listed in an interactive table to the right of the displayed spectrum. Each identified line can then be selected from the table to list corresponding detailed atomic and molecular information. View a SpectroWeb screenshot.

SpectroWeb Software and Releases

SpectroWeb 1.0 is based in part on graphical software packages written nearly a decade ago by Leigh Brookshaw of the Univ. of Southern Queensland, Australia [1]. The Java software packages are written to allow dynamic linking across the Web through an "applet" that loads in any Internet browser for which the Java interpreter has been activated. Java is an object-oriented programming language that has much in common with the C++ programming language.

The SpectroWeb 1.0 interface contains a number of features and improvements over the original graphical Java software with the goal of displaying high-resolution stellar spectra. The software is embedded in Hyper-Text (HTML) language driver programs to facilitate an interactive display of selected spectral regions and for linking an extensive on-line database of related line identifications. The SpectroWeb precompiled Java class files are free for distribution. With it users can provide high-resolution digital spectral atlases and line data online through a fast and user-friendly interactive display.

The SpectroWeb 1.0 database is under permanent development. The team of developers invites everyone who wants to contribute in an effort to further improve the user interaction with SpectroWeb. SpectroWeb 1.0 and an initial spectral line database are currently served online through the Super Dimension Fortress Public Unix webhost in Dallas.

More stars, wavelength regions, and spectral line data will be added to the stellar spectral atlases as time and more disk space become available. The ultimate goal of SpectroWeb is to link and read various stellar atlases in one database that is served from different public websites allover the world using a standardized and commonly approved fast interactive display. New updates and of SpectroWeb 1.0 occur on a regular basis through the SDF Public Webserver.

SpectroWeb 1.0 Observed and Computed High Resolution Solar and Stellar Spectra

The SpectroWeb 1.0 database currently includes a number of observed high-resolution optical spectra of the Sun and bright stars. The high-resolution spectra are observed with very large S/N ratios in on-going observing programs, e. g. with Mercator-Hermes at La Palma. The VLT-UVES spectra are publicly available through the ESO Archive [3] . The spectra have been observed with wavelength resolutions of R~350,000 (KPNO FTS Solar atlas), R~80,000 (VLT-UVES and Mercator-Hermes). They have been converted to the solar and stellar rest wavelength scales to facilitate an accurate comparison with computed spectra (and wavelengths observed in vacuum above 2000 Å are converted to air wavelengths.) The observed fluxes have been continuum normalized for this purpose.

The spectra in SpectroWeb 1.0 are currently computed using a grid of Kurucz stellar atmosphere models that are available online from [4] , and [5]. The list of atomic lines for metals to compute the spectra in LTE is available online from [6] and [7] . Some diatomic molecules have been included to improve the computed position of the stellar continuum level. Note that the computed spectra exclude telluric lines due to water vapor and and O2 in Earth's atmosphere. The strongest H2O and O2 lines are marked in blue color in the observed spectra. It is also important to note that the computed spectra are convolved with a Gaussian filter to simulate the instrumental profile for the observed spectra. Many spectral lines therefore blend together in the computed spectra, which can sometimes be determined from asymmetries in observed spectral features. Users should be cautious that current linelists to compute the spectra are incomplete and many observed spectral features (usually weak absorption lines) require further improvements of the atomic information or have yet to be identified.

SpectroWeb 1.0 Atomic Data and Line Markers

SpectroWeb 1.0 displays numbers (marked with a small arrow) in the observed (solid drawn black line) and computed spectra (solid red line). They are helpful to identify absorption lines and features in the spectra. The markers for atomic lines and corresponding atomic data listed below the spectra are obtained from the Vienna Atomic Line Database [8] . Please note that the theoretical spectra in SpectroWeb are NOT computed with log(gf)-values provided in VALD. The VALD line lists are currently used for marking in the plotted spectra atomic lines useful for the identification of the spectral absorption features.

The line rest wavelengths and log(gf)-values for computing the theoretical spectra in SpectroWeb are permanently updated and further improved. The log(gf)-values of 1178 optical atomic absorption lines in SpectroWeb have been updated with best fits to the observed spectrum of the Sun, Eps Eri, and Procyon. These lines are labeled with L07. Atomic lines labeled in black with L10 list validated atomic data. The computed normalized depths of the validated lines are within 3 % of the normalized line depths observed in these stars. SpectroWeb also lists the computed equivalent line widths for the log(gf)-values of the validated lines, together with the atomic line data we use in the detailed spectral synthesis calculations. The atomic data of all other lines labeled with V-2 are non-validated and have yet to be confirmed with detailed spectral synthesis calculations that correctly fit the observed spectra in SpectroWeb.

SpectroWeb 1.0 to do list October 2010

Further research work is in progress for compiling much more extensive lists in SpectroWeb with empirically validated log(gf)-values (besides the lines currently marked with L07 and L10) based on detailed spectral synthesis calculations of various stars. We are also searching for a high-quality optical spectrum of Canopus to evaluate the log(gf)-values for many more lines of ionic species.

References with Weblinks

[1] Brookshaw, L. 1996, "Java 2D Graph Package, Version 2.4",

[2] Russell, J. P., 2001, "Java Programming for the absolute beginner", Prima Publishing, Roseville, CA

[3] Bagnulo, S., Jehin, E., Ledoux, C., Cabanac, R., Melo, C., Gilmozzi, R., and the ESO Paranal Science Operations Team, 2003, Messenger, 114, 10

[4] Kurucz, R. L. 1993, "ATLAS9 Stellar Atmosphere Programs and 2 km/s grid", Kurucz CD-ROM No. 13, Cambridge, Mass.

[5] Kurucz, R. L. 1994, "Solar Abundance Model Atmospheres for 1, 2, 4, 8 km/s", Kurucz CD-ROM No. 13, Cambridge, Mass.

[6] Kurucz, R. L., and Bell, B., 1995, Kurucz CD-ROM No. 23, Cambridge Mass.

[7] Smith, P. L., Heise, C., Esmond, J. R., and Kurucz, R. L. 1996, "On-Line Atomic and Molecular Data for Astronomy", in UV and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas, K. Yamashita and T. Watanabe, eds., Universal Academy Press, Tokyo, 513

[8] Kupka, F., Piskunov, N. E., Ryabchikova, T. A., Stemples, H. C., Weiss, W. W. 1999, A&AS 139, 119