Package: previs-astro
PREVIS(PythonRequestEngine forVirtualInterferometricSurvey)PREVIS is a Python module that provides functions to help determine the observability of astronomical sources
in a few lines of code.
One can perform a single object search (previs.search) or a multiple-objects search (previs.survey).
These functions use data from the Virtual Observatory (OV), such as:Spectral Energy Distribution (SED) fromVizier.Magnitudes: visible (V, R, G), near-infrared (J, H, K) and mid-infrared (L, M, N). The SED is used to extract the missing magnitudes ofSimbad.
Especially L (3.5 µm), M (4.5 µm), and N (10 µm) magnitudes which are not often included in the standard catalogs,Spectral type,Celestial coordinates,Gaia DR2 informations (if available).PREVIS compares the magnitudes to the current limiting magnitudes of each instruments to determine whether
the target is observable with current performances. The actual instruments are installed at:The european Very Large Telescope Interferometer (VLTI)
withPIONIER(H band),GRAVITY(K band) andMATISSE(L, M, N bands),The american Center for Hight Angular Resolution Astronomy (CHARA), withVEGA(V band),PAVO(R bands),MIRC(H band),CLIMB(K band) andCLASSIC(H, K bands).PREVIS also uses the V or G magnitudes to check the guiding issues or the tip/tilt correction limit.
For the VLTI: if the star is too faint in G mag, PREVIS will look for the list of stars around
the target (57 arcsec) with the appropriate magnitude and give the list of celestial coordinates
usable as guiding star. Of course, PREVIS checks also the on-site observability given the latitude of both observatories.Install from source (for conda-based systems)It is recommended (though not mandatory) to create a separate environment withconda create -n <env_name>.
Then, within your Conda env (conda activate <env_name>):pipinstallprevis-astroWhat can PREVIS do for you?PREVIS is developed and thought to be used in interactive session, so we
recommend to use it into an ipython session. A detailed descriptions of previs
functions and outputs can be found in theapi_reference.mddocument.An example scriptexample.pyis included to test the possibilities offered by PREVIS. The example includes a single target
research usingprevis.search, a visualisation solution for the VLTI (previs.plot_VLTI) and CHARA (previs.plot_CHARA).
The example also presents the survey capabilities of the module.⚡ Last updates (02/2023) : PREVIS is now usable in command line.# Check the observability of Betelgeuse from the VLTI and CHARAprevissearch-tBetelgeuse-p# Same for several targetsprevissurvey-tBetelgeusevega-pNote: you can check input parameters withprevis search -hPREVIScan be used in command line (since v1.0) or through scripts. If you want to simply use theexample.py, you can run it in
interactive session.ipython--matplotlib-iexample.pyFor instance, if you useprevis.searchto fetch data about the star CI Tau, you can display the resulting observability with the VLTI instruments withprevis.plot_VLTI:Such a graph represents multiple informations:Upper left: the name of the target with a green cirle if the star is observable from the VLTI, red if not,Upper right: appropriate magnitudes for the VLTI instruments,The round square at the bottom of the target indicate the information of the guiding star:'Science': the target is bright enought to be used as guiding star,'off axis': the coudé off-axis guiding need to be used,'off axis*', the coudé off-axis guiding can only be performed in visitor mode.The organigram of each instrument:The blue/green octogone indicate the telescope (UT (8m) or AT (1.8m)),The pink circle indicate if fringe tracker (GRA4MAT) is used (ft) or not (noft),The colored squares indicates the observing bands (same color as magnitudes),The right circles are green if the target is observable for each spectral resolution (low (LR), medium (MR) or high (HR)), red if not.Now, if you useprevis.surveyon a large list of stars, e.g: the 666 Wolf-Rayet stars of the galaxy.previs.countindicates that 284 stars are observable from the VLTI (42.6%) and 64 from CHARA (9.6%). You can display the histogram of the result usingprevis.plot_histo_survey:In this case, you can see that those stars are not observable with all instruments and depend of the considered mode. For instance, 20 stars are observables with MATISSE in low spectral resolution with the AT in N band (dark blue bar).The background bars for MATISSE and MIRC indicate respectively, the fringe tracker possibility (GRA4MAT) and the future update MYSTIC operating in K-band. In this case, 152 stars are observable with MATISSE in L-band with the UT but 223 if you use the fringe tracker (see ft/noft ofprevis.searchresult anddesc_survey_large.jpeg).A smaller survey is presented inexample.py, where you can plot the high spectral resolution results (see.desc_survey_example.jpeg).AcknowledgementsPREVIS was developed to help the interferometry user community. I decided to share this simple but useful (hopefully) tool to optimise your time and prepare your futur observing proposals with the VLTI and CHARA. Do not hesitate to raise some undetected problems so far despite our efforts (thanks C. Robert and others).
ENJOY!