The Astropy Project supports and fosters the development of open-source and openly developed Python packages that provide commonly needed functionality to the astronomical community. A key element of the Astropy Project is the core package astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package, as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of interoperable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy Project.

We report on the discovery of HAT-P-11b, the smallest radius transiting extrasolar planet (TEP) discovered from the ground, and the first hot Neptune discovered to date by transit searches. HAT-P-11b orbits the bright (V=9.587) and metal rich ([Fe/H] = +0.31 ± 0.05) K4 dwarf star GSC 03561-02092 with P = 4.8878162 ± 0.0000071 days and produces a transit signal with depth of 4.2 mmag; the shallowest found by transit searches that is due to a confirmed planet. We present a global analysis of the available photometric and radial-velocity data that result in stellar and planetary parameters, with simultaneous treatment of systematic variations. The planet, like its near-twin GJ 436b, is somewhat larger than Neptune (17M ⊕ , 3.8R ⊕ ) both in mass M p = 0.081 ± 0.009 M J (25.8 ± 2.9 M ⊕ ) and radius R p = 0.422 ± 0.014 R J (4.73 ± 0.16 R ⊕ ). HAT-P-11b orbits in an eccentric orbit with e = 0.198 ± 0.046 and ω = 355.2 ± 17.3 • , causing a reflex motion of its parent star with amplitude 11.6 ± 1.2 m s −1 , a challenging detection due to the high level of chromospheric activity of the parent star. Our ephemeris for the transit events is T c = 2454605.89132 ± 0.00032 (BJD), with duration 0.0957 ± 0.0012 d, and secondary eclipse epoch of 2454608.96 ± 0.15 d (BJD). The basic stellar parameters of the host star are M ⋆ = 0.809 +0.020 −0.027 M ⊙ , R ⋆ = 0.752 ± 0.021 R ⊙ and T eff⋆ = 4780 ± 50 K. Importantly, HAT-P-11 will lie on one of the detectors of the forthcoming Kepler mission; this should make possible fruitful investigations of the detailed physical characteristic of both the planet and its parent star at unprecedented precision. We discuss an interesting constraint on the eccentricity of the system by the transit light curve and stellar parameters. This will be particularly useful for eccentric TEPs with low amplitude RV variations in Kepler's field. We also present a blend analysis, that for the first time treats the case of a blended transiting hot Jupiter mimicing a transiting hot Neptune, and proves that HAT-P-11b is not such a blend.

astroquery is a collection of tools for requesting data from databases hosted on remote servers with interfaces exposed on the internet, including those with web pages but without formal application program interfaces (APIs). These tools are built on the Python requests package, which is used to make HTTP requests, and astropy, which provides most of the data parsing functionality. astroquery modules generally attempt to replicate the web page interface provided by a given service as closely as possible, making the transition from browser-based to command-line interaction easy. astroquery has received significant contributions from throughout the astronomical community, including several significant contributions from telescope archives. astroquery enables the creation of fully reproducible workflows from data acquisition through publication. This paper describes the philosophy, basic structure, and development model of the astroquery package. The complete documentation for astroquery can be found at

We report on the latest discovery of the HATNet project: a very hot giant planet orbiting a bright (V ¼ 10:5) star with a small semimajor axis of a ¼ 0:0377 AE 0:0005 AU. Ephemeris for the system is P ¼ 2:2047299 AE 0:0000040 days, midtransit time E ¼ 2;453;790:2593 AE 0:0010 (BJD). Based on the available spectroscopic data on the host star and photometry of the system, the planet has a mass of M p ¼ 1:78 K. Because the host star is quite bright, measurement of the secondary eclipse should be feasible for ground-based telescopes, providing a good opportunity to compare the predictions of current hot Jupiter atmospheric models with the observations. Moreover, the host star falls in the field of the upcoming Kepler mission; hence extensive space-borne follow-up, including not only primary transit and secondary eclipse observations but also asteroseismology, will be possible.

We report the discovery of a massive ( M p ¼ 9:04 AE 0:50 M J ) planet transiting the bright (V ¼ 8:7) F8 star HD 147506, with an orbital period of 5:63341 AE 0:00013 days and an eccentricity of e ¼ 0:520 AE 0:010. From the transit light curve we determine that the radius of the planet is R p ¼ 0:982 þ0:038 À0:105 R J . HD 147506b (also coined HAT-P-2b) has a mass about 9 times the average mass of previously known transiting exoplanets and a density of p % 12 g cm À3 , greater than that of rocky planets like the Earth. Its mass and radius are marginally consistent with theories of structure of massive giant planets composed of pure H and He, and accounting for them may require a large (k100 M È ) core. The high eccentricity causes a ninefold variation of insolation of the planet between peri-and apastron. Using follow-up photometry, we find that the center of transit is T mid ¼ 2;454;212:8559 AE 0:0007 ( HJD) and the transit duration is 0:177 AE 0:002 days.

Using small automated telescopes in Arizona and Hawaii, the HATNet project has detected an object transiting one member of the double star system ADS 16402. This system is a pair of G0 main-sequence stars with age about 3 Gyr at a distance of ∼139 pc and projected separation of ∼1550 AU. The transit signal has a period of 4.46529 days and depth of 0.015 mag. From follow-up photometry and spectroscopy, we find that the object is a "hot Jupiter" planet with mass about 0.53 M J and radius ∼1.36 R J traveling in an orbit with semimajor axis 0.055 AU and inclination about 85. • 9, thus transiting the star at impact parameter 0.74 of the stellar radius. Based on a data set spanning three years, ephemerides for the transit center are: T C = 2453984.397 + N tr * 4.46529. The planet, designated HAT-P-1b, appears to be at least as large in radius, and smaller in mean density, than any previously-known planet.

Using light curves from the HATNet survey for transiting extrasolar planets we investigate the optical broad-band photometric variability of a sample of 27, 560 field K and M dwarfs selected by color and proper-motion (V − K 3.0, µ > 30 mas/yr, plus additional cuts in J − H vs. H − K S and on the reduced proper motion). We search the light curves for periodic variations, and for largeamplitude, long-duration flare events. A total of 2120 stars exhibit potential variability, including 95 stars with eclipses and 60 stars with flares. Based on a visual inspection of these light curves and an automated blending classification, we select 1568 stars, including 78 eclipsing binaries, as secure variable star detections that are not obvious blends. We estimate that a further ∼ 26% of these stars may be blends with fainter variables, though most of these blends are likely to be among the hotter stars in our sample. We find that only 38 of the 1568 stars, including 5 of the eclipsing binaries, have previously been identified as variables or are blended with previously identified variables. One of the newly identified eclipsing binaries is 1RXS J154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, for which we derive preliminary estimates for the component masses and radii of M 1 = M 2 = 0.258 ± 0.008 M ⊙ and R 1 = R 2 = 0.289 ± 0.007 R ⊙ . The radii of the component stars are larger than theoretical expectations if the system is older than ∼ 200 Myr. The majority of the variables are heavily spotted BY Dra-type stars for which we determine rotation periods. Using this sample, we investigate the relations between period, color, age, and activity measures, including optical flaring, for K and M dwarfs, finding that many of the well-established relations for F, G and K dwarfs continue into the M dwarf regime. We find that the fraction of stars that are variable with peak-to-peak amplitudes greater than 0.01 mag increases exponentially with the V − K S color such that approximately half of field dwarfs in the solar neighborhood with M 0.2 M ⊙ are variable at this level. Our data hints at a change in the rotation-activity-age connection for stars with M 0.25 M ⊙ .

We report on the discovery of a planetary system with a close-in transiting hot Jupiter on a near circular orbit and a massive outer planet on a highly eccentric orbit. The inner planet, HAT-P-13b, transits the bright V=10.622 G4 dwarf star GSC 3416-00543 every P = 2.916260±0.000010 days, with transit epoch T c = 2454779.92979 ± 0.00038 (BJD) and duration 0.1345 ± 0.0017 d. The outer planet, HAT-P-13c orbits the star with P 2 = 428.5±3.0 days and nominal transit center (assuming zero impact parameter) of T 2c = 2454870.4 ± 1.8 (BJD) or time of periastron passage T 2,peri = 2454890.05 ± 0.48 (BJD). Transits of the outer planet have not been observed, and may not be present. The host star has a mass of 1.22 +0.05 −0.10 M ⊙ , radius of 1.56 ± 0.08 R ⊙ , effective temperature 5653 ± 90 K, and is rather metal rich with [Fe/H] = +0.41 ± 0.08. The inner planetary companion has a mass of 0.853 +0.029 −0.046 M J , and radius of 1.281±0.079 R J yielding a mean density of 0.498 +0.103 −0.069 g cm −3 . The outer companion has m 2 sin i 2 = 15.2 ± 1.0 M J , and orbits on a highly eccentric orbit of e 2 = 0.691 ± 0.018. While we have not detected significant transit timing variations of HAT-P-13b, due to gravitational and light-travel time effects, future observations will constrain the orbital inclination of HAT-P-13c, along with its mutual inclination to HAT-P-13b. The HAT-P-13 (b,c) double-planet system may prove extremely valuable for theoretical studies of the formation and dynamics of planetary systems.