The subluminous red nova (SLRN) Zwicky Transient Facility (ZTF) SLRN-2020 is the most compelling direct detection of a planet being consumed by its host star, a scenario known as a planetary engulfment event. We present JWST spectroscopy of ZTF SLRN-2020 taken +830 days after its optical emission peak using the NIRSpec fixed-slit 3–5 μ m high-resolution grating and the MIRI 5–12 μ m low-resolution spectrometer. NIRSpec reveals the 12 CO fundamental band ( ν = 1–0) in emission at ∼4.7 μ m, Brackett- α emission, and the potential detection of PH 3 in emission at ∼4.3 μ m. The JWST spectra are consistent with the claim that ZTF SLRN-2020 arose from a planetary engulfment event. We utilize DUSTY to model the late-time ∼1–12 μ m spectral energy distribution (SED) of ZTF SLRN-2020, where the best-fit parameters indicate the presence of warm, 72 0 − 50 + 80 K, circumstellar dust with a total dust mass of Log M d M ⊙ = − 10.6 1 − 0.16 + 0.08 M ⊙ . We also fit a DUSTY model to archival photometry taken +320 days after the peak that suggested the presence of a cooler, T d = 28 0 − 20 + 450 K, and more massive, Log M d M ⊙ = − 5.8 9 − 3.21 + 0.29 , circumstellar dust component. Assuming the cool component originates from the ZTF SLRN-2020 ejecta, we interpret the warm component as fallback from the ejecta. From the late-time SED model, we measure a luminosity of L * = 0.2 9 − 0.06 + 0.03 L ⊙ for the remnant host star, which is consistent with a ∼0.7 M ⊙ K-type star that should not yet have evolved off the main sequence. If ZTF SLRN-2020 was not triggered by stellar evolution, we suggest that the planetary engulfment was due to orbital decay from tidal interactions between the planet and the host star.

Previous Hubble Space Telescope (HST) observations of the star-forming cluster NGC 346 in the Small Magellanic Cloud (SMC) had revealed a large population of pre-main sequence (PMS) candidates, characterised by Halpha excess emission in their photometry. However, without access to spectroscopy, the nature of these objects remained unclear. Using the NIRSpec instrument on board JWST, we studied a sample of these stars, with masses in the range ~0.9-1.8 Msun, effective temperatures in the range 4,500-8,000 K, and PMS ages between ~0.1 and 30 Myr. Here we present the first spectra of solar-mass PMS stars in the metal-poor SMC (Z=1/8 Zsun) and discuss the physical properties of ten representative sources with good signal-to-noise ratio. The observations indicate that even the oldest of these PMS candidates are still accreting gas with typical rates of ~10^{-8} Msun/yr for stars older than ~10 Myr, confirming their PMS nature. The spectra also reveal near-infrared excess and molecular hydrogen excitation lines consistent with the presence of discs around these stars. These findings suggest that in a low-metallicity environment circumstellar discs can live longer than previously thought.

JWST observations of NGC 346, a star-forming region in the metal-poor Small Magellanic Cloud, reveal a substantial population of sub-solar mass young stellar objects (YSOs) with IR excess. We detected $\sim$500 YSOs and pre main sequence (PMS) stars from more than 45,000 unique sources utilizing all four NIRCam wide filters with deep, high-resolution imaging, where ongoing low-mass star formation is concentrated along dust filaments. From these observations, we construct detailed near-IR colour-magnitude diagrams with which preliminary categorizations of YSO classes are made. For the youngest, most deeply-embedded objects, JWST/NIRCam reaches over 10 magnitudes below Spitzer observations at comparable wavelengths, and two magnitudes fainter than HST for more-evolved PMS sources, corresponding to $\sim$0.1 M$_\odot$. For the first time in an extragalactic environment, we detect embedded low-mass star-formation. Furthermore, evidence of IR excess and accretion suggests that dust required for rocky planet formation is present at metallicities as low as 0.2 $Z_\odot$.

Low-mass stars are the most numerous stellar objects in the Universe. Before the James Webb Space Telescope (JWST), we had limited knowledge of how planetary systems around low-mass stars could form at subsolar metallicities. Here we present JWST observations of NGC 346, a star-forming region in the metal-poor Small Magellanic Cloud, revealing a substantial population of subsolar-mass young stellar objects (YSOs) with an infrared excess. We notice that continuing low-mass star formation is concentrated along dust filaments. We detected roughly 500 YSOs and pre-main-sequence (PMS) stars from more than 45,000 unique sources, using all four NIRCam wide filters with deep, high-resolution imaging. From these observations, we construct detailed near-infrared colour–magnitude diagrams with which preliminary categorizations of YSO classes are made. For the youngest, most deeply embedded objects, JWST/NIRCam is ten magnitudes more sensitive than Spitzer observations at comparable wavelengths, and reaches two magnitudes fainter than Hubble Space Telescope for more evolved PMS sources, corresponding to roughly 0.1 M ⊙ . The infrared sensitivity and resolution of JWST allows us to detect embedded low-mass star formation in an extragalactic environment. Furthermore, evidence of infrared excesses and accretion suggests that the dust required for rocky planet formation is present at metallicities as low as 0.2 Z ⊙ , which are akin to those in place at cosmic noon.

We report on James Webb Space Telescope (JWST) commissioning observations of the transiting exoplanet HAT-P-14 b, obtained using the Bright Object Time Series (BOTS) mode of the NIRSpec instrument with the G395H/F290LP grating/filter combination (3–5 μ m). While the data were used primarily to verify that the NIRSpec BOTS mode is working as expected, and to enable it for general scientific use, they yield a precise transmission spectrum which we find is featureless down to the precision level of the instrument, consistent with expectations given HAT-P-14 b’s small scale-height and hence expected atmospheric features. The exquisite quality and stability of the JWST/NIRSpec transit spectrum—almost devoid of any systematic effects—allowed us to obtain median uncertainties of 50–60 ppm in this wavelength range at a resolution of R = 100 in a single exposure, which is in excellent agreement with pre-flight expectations and close to the (or at the) photon-noise limit for a J = 9.094, F-type star like HAT-P-14. These observations showcase the ability of NIRSpec/BOTS to perform cutting-edge transiting exoplanet atmospheric science, setting the stage for observations and discoveries to be made in Cycle 1 and beyond.

The NIRSpec instrument on the James Webb Space Telescope (JWST) brings the first multi-object spectrograph (MOS) into space, enabled by a programmable Micro Shutter Array (MSA) of ∼250,000 individual apertures. During the 6-month Commissioning period, the MSA performed admirably, completing ∼800 reconfigurations with an average success rate of ∼96% for commanding shutters open in science-like patterns. We show that 82.5% of the unvignetted shutter population is usable for science, with electrical short masking now the primary cause of inoperable apertures. In response, we propose a plan to recheck existing shorts during nominal operations, which is expected to reduce the number of affected shutters. We also present a full assessment of the Failed Open and Failed Closed shutter populations, which both show a marginal increase in line with predictions from ground testing. We suggest an amendment to the Failed Closed shutter flagging scheme to improve flexibility for MSA configuration planning. Overall, the NIRSpec MSA performed very well during Commissioning, and the MOS mode was declared ready for science operations on schedule.

The Near-Infrared Spectrograph (NIRSpec) is one of the four focal plane instruments on the James Webb Space Telescope which was launched on Dec. 25, 2021. We present an overview of the as-run NIRSpec commissioning campaign, with particular emphasis on the sequence of activities that led to the verification of all hardware components of NIRSpec. We also discuss the mechanical, thermal, and operational performance of NIRSpec, as well as the readiness of all NIRSpec observing modes for use in the upcoming JWST science program.

NIRSpec is the flagship spectrograph for JWST in the 0.6 to 5.3 micron wavelength range. Observation with the Micro-Shutter Assembly (MSA) for multiobject spectroscopy (MOS) will use configurable shutters to form spectral slits and provide the first space-based MOS capabilities. The NIRSpec Micro-shutter Assembly Target Acquisition (MSATA) is an autonomous target acquisition scheme to acquire and position targets accurately with respect to the spectral slits. The method uses measured centroid positions of reference stars with accurately known relative positions across the target field for this process. MSATA performs not only linear offsets, but any required telescope orient (roll) correction to remove blind-pointing alignment error. The MSATA procedure can be used for most NIRSpec science and will be a prerequisite for most NIRSpec MOS mode observations. Astrometry relating the positions of science targets and candidate reference stars with a relative accuracy of 5 - 10 mas will be needed to deliver the best calibration accuracy of science sources. With this level of planning accuracy, the MSATA procedure should yield a final total pointing accuracy for NIRSpec MOS targets of <20 mas within the preselected 200 mas-wide MSA shutter. Here we present analysis of test cases using simulated datasets that were used to help define and check operations flow for NIRSpec MSATA.

Observations of galaxies across cosmic time show that the star formation rate peaked at a redshift of 1.5, meaning star formation in the Universe occurred predominantly at lower than solar metallicity for which an active burst mode may be more prevalent. However, the overwhelming majority of observational studies have been conducted on solar metallicity Milky Way star formation regions. The question is: Are there substantial differences in the star formation process at lower metallicity? Studies of star forming clouds in reduced metallicity galaxies have been inhibited by the lack of observatories with sufficient resolution and sensitivity. With JWST, we will be able to study star formation in the Magellanic Clouds like we can in the Milky Way with Spitzer. Our Spitzer SAGE and Herschel HERITAGE surveys of the LMC and SMC have revealed where to point JWST to study active star formation from the discovery of …

The Near-Infrared Spectrograph (NIRSpec) is the work-horse spectrograph at 1-5microns for the James Webb Space Telescope (JWST). A showcase observing mode of NIRSpec is the multi-object spectroscopy with the Micro-Shutter Arrays (MSAs), which consist of a quarter million tiny configurable shutters that are 0. ′′20×0. ′′46 in size. The NIRSpec MSA shutters can be opened in adjacent rows to create flexible and positionable spectroscopy slits on prime science targets of interest. Because of the very small shutter width, the NIRSpec MSA spectral data quality will benefit significantly from accurate astrometric knowledge of the positions of planned science sources. Images acquired with the Hubble Space Telescope (HST) have the optimal relative astrometric accuracy for planning NIRSpec observations of 5-10 milli-arcseconds (mas). However, some science fields of interest might have no HST images, galactic fields can have moderate proper motions at the 5mas level or greater, and extragalactic images with HST may have inadequate source information at NIRSpec wavelengths beyond 2 microns. Thus, optimal NIRSpec spectroscopy planning may require pre-imaging observations with the Near-Infrared Camera (NIRCam) on JWST to accurately establish source positions for alignment with the NIRSpec MSAs. We describe operational philosophies and programmatic considerations for acquiring JWST NIRCam pre-image observations for NIRSpec MSA spectroscopic planning within the same JWST observing Cycle.

We report accelerated aging tests on three Pt/Ne lamps from the same manufacturing run as lamps installed on the Cosmic Origins Spectrograph (COS). One lamp was aged in air at the National Institute of Standards and Technology (NIST) at a current of 10 mA and 50% duty cycle (30 s on, 30 s off) until failure. Two other lamps were aged by the COS instrument development team in a vacuum chamber. Initial radiometrically calibrated spectra were taken of all three lamps at NIST. Calibrated spectra of the air-aged lamp were taken after 206, 500, 778, 783 and 897 hr of operation. Spectra of the vacuum-aged lamps were taken after 500 hr for both lamps, and after 1000 hr for one of the lamps. During vacuum aging, the lamp voltage, photometric stability and temperature were monitored. All three lamps lasted for over 900 hr (100,000 cycles) when run at 10 mA, sufficient for 10–12 years of operation on COS. The total output dropped by less than 15% over 500 hr, with short-term repeatability within a few percent. We recommend that future space operation of these lamps include the lamp voltage in the telemetry as a diagnostic for the lamp aging.

We describe the COS NUV imaging performance as derived from data taken during the Observatory Verification period after HST Servicing Mission #4. This includes photometric growth curves using data taken with the two available MIRROR settings (MIRRORA and MIRRORB) and the PSA and BOA apertures, throughput and image quality as function of spatial offset from the center of the COS aperture, and a description of the imaging-mode point spread function (PSF). The observed PSF is fully consistent with the model (at good HST focus), except for two minor ghosts located about 20 pixels away from the PSF center. A comparison of imaging observations of a cool and a hot flux standard star reveals a significantly higher red sensitivity of the COS imaging modes than that predicted from ground calibration data. Apart from that, the results are roughly consistent with predictions from ground calibration. The new throughput curves are used in the COS imaging and imaging target acquisition exposure time calculators since October 7, 2009.

After the initial on-orbit determination of spectroscopic sensitivities was made for the near ultraviolet (NUV) and far ultraviolet (FUV) channels on the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST), additional monitoring has continued in Cycle 17 as part of the Cycle 17 COS Calibration Program. Lowand medium-resolution gratings are observed roughly monthly and quarterly, respectively, using external observations of spectrophotometric standard stars.

The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope (HST) during Servicing Mission 4 (SM4) in May 2009. COS is designed to obtain spectra of faint objects at moderate spectral resolution (R > 16,000) in two channels: FUV, covering wavelengths from 1150 to 1450 angstrom; and NUV, covering 1700 - 3200 angstrom. Two low resolution gratings (R > 1500) cover the < 900 - 2050 angstrom (FUV) and 1650 - 3200 angstrom (NUV) wavelength regions. An imaging capability is also available on the NUV channel.As part of the Hubble Servicing Mission Observatory Verification (SMOV) program, an extensive period of checkout, fine-tuning and preliminary characterization began after the installation of COS. The COS SMOV program was a cooperative effort between the Space Telescope Science Institute and the Instrument Definition Team based at the University of Colorado. Nearly 2800 COS exposures in 34 separate observing programs were obtained during the course of SMOV. Early activities included an initial instrument functional checkout, turn-on and initial characterization of the detectors, NUV and FUV channel focus and alignment, and target acquisition verification and assessment. Once this initial period was completed, science-related calibrations and verifications were performed in order to prepare the instrument for normal science operations. These activities included wavelength calibration, flux calibration, detector flat field characterization, spectroscopic performance verification, high S/N operation, and thermal and structural stability measurements. We discuss the design, execution and results of the SMOV program, including the interrelationships between the various tasks, and how the pre-launch plan was adjusted in real-time due to changing conditions.

By reverse engineering the actions performed by COS TAs, we have been able to approximate the blind pointing accuracy of HST+COS. The mean blind pointing offset in [AD,XD] coordinates was [-0.24±0.51, -0.17±68]", indicating a possible offset in the FGS to COS alignment. The outer black dashed circle in the figure below represents the R=1.25" aperture, the red dotted circle is the centering limit to transmit maximum flux, the blue dashed circle is the FUV centering goal (0.106”), and the black solid circle is the NUV centering goal (0.41”).