We present an analysis of the host-galaxy environment of Swope Supernova Survey 2017a (SSS17a), the discovery of an electromagnetic counterpart to a gravitational-wave source, GW170817. SSS17a occurred 1.9. kpc (in projection; 10 ''.2) from the nucleus of NGC. 4993, an S0 galaxy at a distance of 40. Mpc. We present a Hubble Space Telescope (HST) pre-trigger image of NGC. 4993, Magellan optical spectroscopy of the nucleus of NGC. 4993 and the location of SSS17a, and broadband UV-through-IR photometry of NGC. 4993. The spectrum and broadband spectral-energy distribution indicate that NGC. 4993 has a stellar mass of log(M/M-circle dot) 10.49(-0.20) (+0.08) and star formation rate of 0.003 M-circle dot yr(-1), and the progenitor system of SSS17a likely had an age of >2.8. Gyr. There is no counterpart at the position of SSS17a in the HST pre-trigger image, indicating that the progenitor system had an absolute magnitude M-V > -5.8 mag. We detect dust lanes extending out to almost the position of SSS17a and >100 likely globular clusters associated with NGC. 4993. The offset of SSS17a is similar to many short gamma-ray-burst offsets, and its progenitor system was likely bound to NGC. 4993. The environment of SSS17a is consistent with an old progenitor system such as a binary neutron star system.

Las Campanas Observatory (LCO) of the Carnegie Institution of Science has been operating in Chile for about 50 years, currently operating four main telescopes. Carnegie operates the two 6.5 meter Magellan telescopes on behalf of a partnership that includes a consortium of universities. The Magellan Telescopes were commissioned in 2000 and 2002 and offer the consortium users a suite of twelve instruments. In this paper we will first provide a brief description of the science, technical and administrative structure of the observatory. We will then present an updated review of the Magellan telescopes operations and maintenance. Details on status and performances of the instruments will be given. We will finally cover the operations of the duPont 2.5 meter and Swope 1 meter telescopes including the current and future collaboration with the two hemisphere surveys SDSS-IV and SDSS-V.

We report the discovery of HATS-70b, a transiting brown dwarf at the deuterium burning limit. HATS-70b has a mass of M p = 12.9(-1.6)(+1.8) M-Jup and a radius of R-p = 1.384(-0.074) (+ 0.079) R-Jup, residing in a close-in orbit with a period of 1.89 days. The host star is a /14 * = 1.78 +/- 0.12 M-circle dot A star rotating at v sin I-* = 40.61(-0.35)(+0.32) km s( -1) , enabling us to characterize the spectroscopic transit of the brown dwarf via Doppler tomography. We find that HATS-70b, like other massive planets and brown dwarfs previously sampled, orbits in a low projected-obliquity orbit with lambda = 8.9(-4.5)+(5.6)(degrees). The low obliquities of these systems is surprising given all brown dwarf and massive planets with obliquities measured orbit stars hotter than the Kraft break. This trend is tentatively inconsistent with dynamically chaotic migration for systems with massive companions, though the stronger tidal influence of these companions makes it difficult to draw conclusions on the primordial obliquity distribution of this population. We also introduce a modeling scheme for planets around rapidly rotating stars, accounting for the influence of gravity darkening on the derived stellar and planetary parameters.

We present an optical transmission spectrum of the atmosphere of WASP-4b obtained through observations of four transits with Magellan/IMACS, as part of the Arizona-CfA-Catolica-Carnegie Exoplanet Spectroscopy Survey (ACCESS). Using a Bayesian approach to atmospheric retrieval, we find no evidence for scattering or absorption features in our transit spectrum. Our models include a component to model the transit light source effect (spectral contamination from unocculted spots on the stellar photosphere), which we show can have a marked impact on the observed transmission spectrum for reasonable spot-covering fractions (<5%); this is the first such analysis for WASP-4b. We are also able to fit for the size and temperature contrast of spots observed during the second and third transits, finding evidence for both small, cool and large, warm spot-like features on the photosphere. Finally, we compare our results to those published by Huitson et al. using Gemini/GMOS and May et al. using IMACS, and we find that our data are in agreement.

We report the discovery of K2-287b, a Saturn mass planet orbiting a G-dwarf with a period of P approximate to 15 days. First uncovered as a candidate using K2 campaign 15 data, follow-up photometry and spectroscopy were used to determine a mass M-p = 0.317 +/- 0.026 M-J, radius R-p = 0.833 +/- 0.013 R-J, period P = 14.893291 +/- 0.000025 days, and eccentricity e = 0.476 +/- 0.026. The host star is a metal-rich V = 11.410 +/- 0.129 mag G-dwarf for which we estimate a mass M-* = 1.056(-0.021)(+0.022) M-circle dot, radius R-* = 1.070 +/- 0.010 R-circle dot, metallicity [Fe/H] = 0.20 +/- 0.05, and T-eff = 5673 +/- 75 K. This warm eccentric planet with a time-averaged equilibrium temperature of T-eq approximate to 800 K adds to the small sample of giant planets orbiting nearby stars whose structure is not expected to be affected by stellar irradiation. Follow-up studies on the K2-287 system could help constrain theories of planet migration in close-in orbits.

We present new eclipse observations for one of the hottest 'hot Jupiters', WASP-18b, for which previously published data from HST WFC3 and Spitzer have led to radically conflicting conclusions about the composition of this planet's atmosphere. We measure eclipse depths of 0.15 +/- 0.02 per cent at Ks and 0.07 +/- 0.01 per cent at i bands. Using the VSTAR line-by-line radiative transfer code and both these new observations with previously published data, we derive a new model of the planetary atmosphere. We have varied both the metallicity and C/O ratio in our modelling, and find no need for the extreme metallicity suggested by Sheppard et al. Our best-fitting models slightly underestimate the emission at i band and overestimate the observed flux at Ks band. To explain these discrepancies, we examine the impact on the planetary emission spectrum of the presence of several types of hazes which could form on the night side of the planet. Our Ks-band eclipse flux measurement is lower than expected from clear atmosphere models and this could be explained by haze particles larger than 0.2 mu m with the optical properties of Al2O3, CaTiO3 or MgSiO3. We find that z'-band measurements are important for understanding the contribution of photochemical hazes with particles smaller than 0.1 mu m at the top of the atmosphere.

We report on the confirmation of a transiting giant planet around the relatively hot (T-eff = 6801 +/- 76 K) star HD 2685, whose transit signal was detected in Sector 1 data of NASA's TESS mission. We confirmed the planetary nature of the transit signal using Doppler velocimetric measurements with CHIRON, CORALIE, and FEROS, as well as using photometric data obtained with the Chilean-Hungarian Automated Telescope and the Las Cumbres Observatory. From the joint analysis of photometry and radial velocities, we derived the following parameters for HD 2685 b: P =4.12688(-0.00004)(+0.00005) days, e =0.091(-0.047)(+0.039), Mp = 1.17 +/- 0.12 M-J, and R-p =1.44 +/- 0.05 R-J. This system is a typical example of an inflated transiting hot Jupiter in a low-eccentricity orbit. Based on the apparent visual magnitude (V = 9.6 mag) of the host star, this is one of the brightest known stars hosting a transiting hot Jupiter, and it is a good example of the upcoming systems that will be detected by TESS during the two-year primary mission. This is also an excellent target for future ground- and space-based atmospheric characterization as well as a good candidate for measuring the projected spin-orbit misalignment angle through the Rossiter-McLaughlin effect.

The short-period (0.94-d) transiting exoplanet WASP-19b is an exceptional target for transmission spectroscopy studies, due to its relatively large atmospheric scale height (similar to 500 km) and equilibrium temperature (similar to 2100 K). Here, we report on six precise spectroscopic Magellan/IMACS observations, five of which target the full optical window from 0.45 to 0.9 mu m and one targeting the 0.4-0.55 mu m blue-optical range. Five of these data sets are consistent with a transmission spectrum without any significant spectral features, while one shows a significant slope as a function of wavelength, which we interpret as arising from photospheric heterogeneities in the star. Coupled with HST/WFC3 infrared observations, our optical/near-infrared measurements point to the presence of high altitude clouds in WASP-19b's atmosphere in agreement with previous studies. Using a semi-analytical retrieval approach, considering both planetary and stellar spectral features, we find a water abundance consistent with solar for WASP-19b and strong evidence for sub-solar abundances for optical absorbers such as TiO and Na; no strong optical slope is detected, which suggests that if hazes are present, they are much weaker than previously suggested. In addition, two spot-crossing events are observed in our data sets and analysed, including one of the first unambiguously detected bright-spot-crossing events on an exoplanet host star.

We present the discovery of TYC9191-519-1b (TOI-150b, TIC 271893367) and HD271181b (TOI-163b, TIC 179317684), two hot Jupiters initially detected using 30-min cadence Transiting Exoplanet Survey Satellite (TESS) photometry from Sector 1 and thoroughly characterized through follow-up photometry (CHAT, Hazelwood, LCO/CTIO, El Sauce, TRAPPIST-S), high-resolution spectroscopy (FEROS, CORALIE), and speckle imaging (Gemini/DSSI), confirming the planetary nature of the two signals. A simultaneous joint fit of photometry and radial velocity using a new fitting package JULIET reveals that TOI-150b is a 1.254 +/- 0.016 R-J, massive (2.61(-0.12)(+0.19) M-J) hot Jupiter in a 5.857-d orbit, while TOI-163b is an inflated (R-P = 1.478(-0.029)(+0.022) R-J, M-P = 1.219 +/- 0.11 M-J) hot Jupiter on a P = 4.231-d orbit; both planets orbit F-type stars. A particularly interesting result is that TOI-150b shows an eccentric orbit (e = 0.262(-0.037)(+0.045)), which is quite uncommon among hot Jupiters. We estimate that this is consistent, however, with the circularization time-scale, which is slightly larger than the age of the system. These two hot Jupiters are both prime candidates for further characterization - in particular, both are excellent candidates for determining spin-orbit alignments via the Rossiter-McLaughlin (RM) effect and for characterizing atmospheric thermal structures using secondary eclipse observations considering they are both located closely to the James Webb Space Telescope (JWST) Continuous Viewing Zone (CVZ).

We present a new ground-based visual transmission spectrum of the hot Jupiter WASP-43b, obtained as part of the ACCESS Survey. The spectrum was derived from four transits observed between 2015 and 2018, with combined wavelength coverage between 5300 and 9000 A and an average photometric precision of 708 ppm in 230 A bins. We perform an atmospheric retrieval of our transmission spectrum combined with literature Hubble Space Telescope/WFC3 observations to search for the presence of clouds/hazes as well as Na, K, H alpha, and H2O planetary absorption and stellar spot contamination over a combined spectral range of 5318-16420 A. We do not detect a statistically significant presence of Na i or K i alkali lines, or H alpha in the atmosphere of WASP-43b. We find that the observed transmission spectrum can be best explained by a combination of heterogeneities on the photosphere of the host star and a clear planetary atmosphere with H2O. This model yields a log evidence of 8.26 0.42 higher than a flat (featureless) spectrum. In particular, the observations marginally favor the presence of large, low-contrast spots over the four ACCESS transit epochs with an average covering fraction T = 132 K 132 K. Within the planet's atmosphere, we recover a log H2O volume mixing ratio of -2.78(-1.47)(+1.38), which is consistent with previous H2O abundance determinations for this planet.