arXiv subjects

Charlie Hull

Publications and source records attributed to Charlie Hull.

3 recordsLinked to original sources

arXiv2026

Update on the slicer IFU for the Magellan InfraRed Multi-Object Spectrograph (MIRMOS)

The Magellan InfraRed Multi-Object Spectrograph (MIRMOS) is a planned next generation multi-object and integral field spectrograph for the 6.5m Magellan telescopes at Las Campanas Observatory in Chile. MIRMOS will perform $\rm R\sim3700$ spectroscopy over a simultaneous wavelength range of 0.886 - 2.404um (Y, J, H, K bands) in addition to imaging over the range of 0.7 - 0.886um. The integral field mode of operation for MIRMOS will be achieved via an image slicer style integral field unit (IFU) located on a linear stage to facilitate movement into the beam during use or storage while operating in multi-object mode. The IFU will provide an $\rm\sim18''\times26''$ field of view (FoV) made up of $\rm0.84''\times26''$ slices. This will be the largest FoV IFS operating at these wavelengths from either the ground or space, making MIRMOS an ideal instrument for a wide range of science cases including studying the high redshift circumgalactic medium and emission line tracers from ionized and molecular gas in nearby galaxies. We present here an update on the IFU design from our 2024 proceeding. Previously we utilized a re-imaging style slicer which required freeform pupil mirrors in order to achieve the required image quality while obeying significant packaging constraints near the instrument focal surface. In order to reduce the manufacturing cost and decouple the IFU from the configurable slit unit used in multi-object mode, we have moved the IFU deeper into the instrument, allowing for a switch to a virtual style IFU. This now requires a re-imaging doublet before the slicer mirrors, but removes the need for any freeform surfaces. We present here the optical design and predicted performance of the new MIRMOS IFU along with a conceptual design for the opto-mechanical system which will move the IFU between its active and stored positions.

astro-ph.IM↗

arXiv2026

Update on the Magellan InfraRed Multi-Object Spectrograph (MIRMOS)

The Magellan InfraRed Multi-Object Spectrograph (MIRMOS) will be a next generation multi-object (MOS) and integral field spectrograph (IFS) for the 6.5m Magellan telescopes at Las Campanas Observatory in Chile. MIRMOS will perform R~3700 spectroscopy over a simultaneous wavelength range of 0.886-2.404um (Y, J, H, and K bands) in addition to imaging over the range of 0.7-0.886um. Target selection in the MOS mode is achieved through a cryogenic mechanism capable of making up to 92 slits over a 13'x3' field of view (FoV). This mechanism can be reconfigured in real time to adjust slit widths for seeing conditions, change to a different mask, or form a long slit. The IFS mode of operation for MIRMOS will be achieved via an image slicer style integral field unit (IFU) which will provide an ~18"x26" FoV made up of 0.84"x26" slices. MIRMOS's design will allow it to address a wide range of science cases from performing spectroscopy of high-redshift galaxies as well as high signal-to-noise transmission spectroscopy of exoplanet atmospheres with the MOS/long slit mode, while also having the largest FoV IFS operating on a large telescope at these wavelengths. We will describe here the design of the MIRMOS instrument -- now at the end of the preliminary design phase.

astro-ph.IM↗

arXiv2024

A High-Resolution Non-Detection of Escaping Helium In The Ultra-Hot Neptune LTT 9779b: Evidence for Weakened Evaporation

The recent discovery of ``ultra-hot'' ($P < 1$ day) Neptunes has come as a surprise: some of these planets have managed to retain gaseous envelopes despite being close enough to their host stars to trigger strong photoevaporation and/or Roche lobe overflow. Here, we investigate atmospheric escape in LTT 9779b, an ultra-hot Neptune with a volatile-rich envelope. We observed two transits of this planet using the newly-commissioned WINERED spectrograph ($R\sim68,000$) on the 6.5 m Clay/Magellan II Telescope, aiming to detect an extended upper atmosphere in the He 10830 A triplet. We found no detectable planetary absorption: in a 0.75 A passband centered on the triplet, we set a 2$\sigma$ upper limit of 0.12% ($\delta R_p/H < 14$) and a 3$\sigma$ upper limit of 0.20% ($\delta R_p/H < 22$). Using a H/He isothermal Parker wind model, we found corresponding 95% and 99.7% upper limits on the planetary mass-loss rate of $\dot{M} < 10^{10.03}$ g s$^{-1}$ and $\dot{M} < 10^{11.11}$ g s$^{-1}$ respectively, smaller than predicted by outflow models even considering the weak stellar XUV emission. The low evaporation rate is plausibly explained by a metal-rich envelope, which would decrease the atmospheric scale height and increase the cooling rate of the outflow. This hypothesis is imminently testable: if metals commonly weaken planetary outflows, then we expect that \textit{JWST} will find high atmospheric metallicities for small planets that have evaded detection in He 10830 A.

astro-ph.EP↗