Here, we present an astrophotonic spectrograph in the near-IR H-band (1.45 -1.65 µm) and a spectral resolution (λ/δλ) of 1500. The main dispersing element of the spectrograph is a photonic chip based on Arrayed-Waveguide-Grating technology. The 1D spectrum produced on the focal plane of the AWG contains overlapping spectral orders, each spanning a 10 nm band in wavelength. These spectral orders are cross-dispersed in the perpendicular direction using a cross-dispersion setup which consists of collimating lenses and a prism and the 2D spectrum is thus imaged onto a near-IR detector. Here, as a proof of concept, we use a few-mode photonic lantern to capture the light and feed the emanating single-mode outputs to the AWG chip for dispersion. The total size of the setup is 50×30×20 cm 3 , nearly the size of a shoebox. This spectrograph will pave the way for future miniaturized integrated photonic spectrographs on large telescopes, particularly for building future photonic multi-object spectrographs.

AT 2016dah and AT 2017fyp are fairly typical Andromeda galaxy (M 31) classical novae. AT 2016dah is an almost text book example of a ‘very fast’ declining, yet uncommon, Fe ii‘b’ (broad-lined) nova, discovered during the rise to peak optical luminosity, and decaying with a smooth broken power-law light curve. AT 2017fyp is classed as a ‘fast’ nova, unusually for M 31, its early decline spectrum simultaneously shows properties of both Fe ii and He/N spectral types – a ‘hybrid’. Similarly, the light curve of AT 2017fyp has a broken power-law decline but exhibits an extended flat-topped maximum. Both novae were followed in the UV and X-ray by the Neil Gehrels Swift Observatory, but no X-ray source was detected for either nova. The pair were followed photometrically and spectroscopically into their nebular phases. The progenitor systems were not visible in archival optical data, implying that the mass donors are main-sequence stars. What makes AT 2016dah and AT 2017fyp particularly interesting is their position with respect to M 31. The pair are close on the sky but are located far from the centre of M 31, lying almost along the semiminor axis of their host. Radial velocity measurements and simulations of the M 31 nova population leads to the conclusion that both novae are members of the Andromeda Giant Stellar Stream (GSS). We find the probability of at least two M 31 novae appearing coincident with the GSS by chance is $\sim \!1{{\ \rm per\ cent}}$. Therefore, we claim that these novae arose from the GSS progenitor, not M 31 – the first confirmed novae discovered in a tidal steam.

The Circumgalactic Hα Spectrograph (CHαS) is a ground-based optical integral field spectrograph designed to detect ultrafaint extended emission from diffuse ionized gas in the nearby universe. CHαS is particularly well suited for making direct detections of tenuous Hα emission from the circumgalactic medium (CGM) surrounding low-redshift galaxies. It efficiently maps large regions of the CGM in a single exposure, targeting nearby galaxies (d < 35 Mpc) where the CGM is expected to fill the field of view. We are commissioning CHαS as a facility instrument at MDM Observatory. CHαS is deployed in the focal plane of the Hiltner 2.4 m telescope, utilizing nearly all of the telescope’s unvignetted focal plane (10′–15′) to conduct wide-field spectroscopic imaging. The catadioptric design provides excellent wide-field imaging performance. CHαS is a pupil-imaging spectrograph employing a microlens array to divide the field of view into >60,000 spectra. CHαS achieves an angular resolution of [1.3–2.6] arcseconds and a resolving power of R = [10,000–20,000]. Accordingly, the spectrograph can resolve structure on the scale of 1–5 kpc (at 10 Mpc) and measure velocities down to 15–30 km s−1. CHαS intentionally operates over a narrow (30 Å) bandpass; however, it is configured to adjust the central wavelength and target a broad range of optical emission lines individually. A high–diffraction efficiency volume phase holographic grating ensures high throughput across configurations. CHαS maintains a high grasp and moderate spectral resolution, providing an ideal combination for mapping discrete, ultralow–surface brightness emission on the order of a few milli-Rayleigh.