Adding JOSS paper

docs/paper.bib

@@ -0,0 +1,40 @@
+
+@ARTICLE{Snellen:2010,
+       author = {{Snellen}, Ignas A.~G. and {de Kok}, Remco J. and
+         {de Mooij}, Ernst J.~W. and {Albrecht}, Simon},
+        title = "{The orbital motion, absolute mass and high-altitude winds of exoplanet HD209458b}",
+      journal = {\nat},
+     keywords = {Astrophysics - Earth and Planetary Astrophysics},
+         year = "2010",
+        month = "Jun",
+       volume = {465},
+       number = {7301},
+        pages = {1049-1051},
+          doi = {10.1038/nature09111},
+archivePrefix = {arXiv},
+       eprint = {1006.4364},
+ primaryClass = {astro-ph.EP},
+       adsurl = {https://ui.adsabs.harvard.edu/abs/Snellen2010},
+      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
+}
+
+
+@ARTICLE{Brogi:2012,
+       author = {{Brogi}, Matteo and {Snellen}, Ignas A.~G. and {de Kok}, Remco J. and
+         {Albrecht}, Simon and {Birkby}, Jayne and {de Mooij}, Ernst J.~W.},
+        title = "{The signature of orbital motion from the dayside of the planet {\ensuremath{\tau}} Bo{\"o}tis b}",
+      journal = {\nat},
+     keywords = {Astrophysics - Earth and Planetary Astrophysics},
+         year = "2012",
+        month = "Jun",
+       volume = {486},
+       number = {7404},
+        pages = {502-504},
+          doi = {10.1038/nature11161},
+archivePrefix = {arXiv},
+       eprint = {1206.6109},
+ primaryClass = {astro-ph.EP},
+       adsurl = {https://ui.adsabs.harvard.edu/abs/Brogi2012},
+      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
+}
+

docs/paper.md

@@ -0,0 +1,59 @@
+---
+title: 'hipparchus: Cross-correlation functions via the weighted mean'
+tags:
+  - Python
+  - astronomy
+  - high resolution spectroscopy
+authors:
+  - name: Brett M. Morris
+    orcid: 0000-0003-2528-3409
+    affiliation: 1
+affiliations:
+ - name: Center for Space and Habitability, University of Bern, Switzerland
+   index: 1
+date: January 2020
+bibliography: paper.bib
+
+aas-doi: 10.3847/xxxxx
+aas-journal: Astrophysical Journal
+---
+
+# Summary
+
+The presence of starspots on exoplanet host stars potentially hinders the 
+interpretation of planet observations. We must know the starspot covering 
+fractions of stars in order to interpret the transmission and day-side 
+spectra of small exoplanets, because the spectral features generated by 
+exoplanet atmospheres are degenerate with the signatures of starspots. If we 
+seek to measure starspot coverages with sufficient precision to mitigate
+the effects of starspots on planet characterization, we must develop new 
+techniques to measure the spatial extent of starspots. This is difficult to do 
+in practice because starspots are dim compared to the rest of the stellar 
+photosphere, and take up a small fraction of the stellar surface area. 
+
+An analogous contrast-ratio problem occurs when detecting the emission or 
+transmission spectra from exoplanet atmospheres, which has been addressed using
+the cross-correlation function (CCF) technique applied to high resolution 
+spectroscopy [@Snellen:2010, @Brogi:2012]. The CCF is sensitive to both strong 
+and weak absorption features that occur at *all* wavelengths throughout the 
+spectrum of the planet, constructively co-adding the absorption lines into a 
+single average when a template spectrum is matched with the observed spectrum
+at the correct Doppler velocity.
+
+We introduce ``hipparchus``, a pure Python, open source package designed for
+cross-correlating HARPS with synthetic spectral templates. The 
+accompanying submitted paper to AAS Journals applies the package to the problem
+of hunting for cool starspots on stellar photospheres, but it could be used
+more generally to measure the CCF in a variety of contexts. ``hipparchus`` 
+computes the CCF via the weighted mean, with the help of array broadcasting to 
+simultaneously compute the CCF efficiently at many velocities. It includes
+convenience functions for reading and continuum normalizing HARPS(-N) E2DS 
+spectra, along with an object-oriented framework for computing CCFs. 
+Contributions to ``hipparchus`` from the community are welcome.
+
+# Acknowledgements
+
+We acknowledge valuable advice from H. Jens Hoeijmakers, and spectral templates
+from Daniel Kitzmann.
+
+# References