Astrocombs are highly precise optical reference systems used for astronomical spectrograph calibration, enabling accurate and consistent measurement of stellar absorption line frequencies across a broad spectral range. By comparing a star's spectrum to the astrocomb spectrum, minute radial velocity shifts indicative of an exoplanet's presence can be detected. The highest precision and accuracy astrocombs are generated by laser frequency combs. However, in the visible band, frequency comb calibrators have stringent operational lifetime limitations due to degradation of the supercontinuum-generating medium, and are thus typically used to calibrate Fabry-P & eacute;rot etalons, which are then used for simultaneous observations with target stars. This work demonstrates a specially designed crystalline whispering-gallery-mode resonator (WGMR) that serves as an astrocomb etalon, featuring a coupling wavelength span of two octaves and a quasi-single-mode family. Several innovations have been incorporated into the system's compact design to achieve frequency stability, in addition to wide-range wavelength coupling. These include dual-mode thermometric frequency stabilization, in addition to vacuum packaging, effectively minimizing thermal and pressure-induced frequency drift. Long-term frequency stability, measured via a heterodyne RF beat note, exceeds 2 & times; 10-12, with a projected long-term modal frequency stability of less than or similar to 10-10 (equivalently 3 cm/s in Doppler velocity). This level of stability obviates the need for frequent cross-calibration with a laser reference, as was required with other astrocomb etalons. Overall, the architecture of the WGMR etalon provides a new and powerful capability, beyond what has previously been achieved by microresonator-based etalons, as a compact, ultra-wideband spectral reference for detecting small planets in long-period orbits around nearby stars. It also offers a path forward for a low size, weight, and power (SWaP) spectral reference appropriate for spaceflight. (c) 2026 Chinese Laser Press

We present a Hubble Space Telescope (HST) imaging survey of a 1.1 deg ^2 sky area toward the Milky Way Galactic bulge. This field significantly overlaps with the upcoming Nancy Grace Roman Galactic Bulge Time Domain Survey. High angular resolution imaging of this area with HST before the start of the Roman Galactic Exoplanet Survey will greatly strengthen Roman’s ability to characterize detected exoplanet systems, as well as provide a rich and wide-field archive for use as a legacy dataset toward the Galactic bulge for the broader community. We conduct coordinated parallel imaging with both wide-field cameras on HST, the Wide Field Camera 3 and Advanced Camera for Surveys, utilizing the F606W and F814W passbands. Approximately 70% of the survey was conducted during HST Cycle 32, with the remaining 30% conducted during Cycle 33. In this Letter, the first in a series, we give a general overview of the program and the observing strategy and present early results. This campaign secures HST’s lasting impact on the high-precision study of stellar populations, dynamics, exoplanet systems, interstellar extinction, metallicities, cluster associations, and more toward the center of our Galaxy.

We observed the HR 8799 planetary system with JWST's NIRCam instrument using its F356W and F444W filters to search for additional, lower-mass planets that might reside between or exterior to the four previously detected Jovian-mass planets. After blocking out the star with a circular occulting mask with gradual radial opacity, the four known planets (b, c, d, and e) are detected in both filters, even though the innermost planet lies so close to its parent star that the coronagraphic mask nominally blocks similar to 86% of the planet's light. The observed fluxes and positions of the planets are consistent with previous models of the planets' atmospheres and with predictions of orbital fits. Two background sources are detected interior to and within the outer debris ring, respectively, both of which are visible in ALMA images at submillimeter wavelengths. No new planet candidates >= 1 MJup are seen within the region defined by the four known planets. Planets larger than a Saturn mass (similar to 0.3 MJup) are ruled out within the outer gap between HR 8799 b (at 70 au) and the cold belt of debris (>= 120 au), limiting the ability of a potential planet in that region to sculpt the inner edge of the outer disk.

Studying cold brown dwarfs is key to understanding the diverse characteristics of cold giant exoplanets atmospheres. COCONUTS-2 is a wide binary system composed of a T9 brown dwarf and an M3 star, which presents a unique opportunity to characterize a cold benchmark brown dwarf. As part of a JWST program to study the range of physical and atmospheric properties of the coldest brown dwarfs, we obtained NIRSpec G395H spectra ( R ∼ 2700, 2.87−5.13 μ m) and MIRI F1000W, F1280W, and F1800W photometry for COCONUTS-2 b. In this work, we find a 99% probability of the system belonging to the Corona of Ursa Major moving group (414 ± 23 Myr) using BANYAN Σ and its full kinematics. We also reestimate the astrometry of COCONUTS-2b using the MIRI data. We support this membership with a comparison of the rotation period, metallicity, and C/O ratio of the group with those of the COCONUTS-2 system. We also calculate its bolometric luminosity, which, combined with our age estimation, allows us to derive its mass, effective temperature, surface gravity, and radius with high precision. As a result of our analysis, we support the conclusion that COCONUTS-2 b is a planetary-mass object (7.5 ± 0.4 M _Jup ), which was likely formed via the same mechanism as stars. In addition we compare the JWST spectrum to another object in the sample, J082507.35+280548.5 (0825+2805), a Y0.5 brown dwarf, which is a candidate member of the same moving group, but has a lower mass (3.7 ± 0.2 M _Jup ). We identify absorption feature differences, which could indicate that 0825+2805 has stronger vertical mixing.

Brown dwarfs lack nuclear fusion and cool with time; the coldest known have an effective temperature below 500 K, and are known as Y dwarfs. We present a James Webb Space Telescope (JWST) photometric data set of Y dwarfs: 23 were imaged in wide-field mode, 20 using NIRCam with the F150W and F480M filters, and three using NIRISS with the F480M filter. We present an F480M versus F150W – F480M color–magnitude diagram for our sample, and other brown dwarfs with F150W and F480M colors synthesized from JWST spectra by S. A. Beiler et al. For one target, WISEA J083011.95+283716.0, its detection in the near-infrared confirms it as one of the reddest Y dwarfs known, with F150W – F480M = 9.62 mag. We provide its updated parallax and proper motion. One of the Beiler et al. Y dwarfs, CWISEP J104756.81+545741.6, is unusually blue, consistent with strong CO absorption seen in its spectrum, which the F480M filter is particularly sensitive to. The strong CO and the kinematics of the object suggest it may be very low mass and young. We update the resolved photometry for the close binary system WISE J033605.05–014350.4 AB, and find that the secondary is almost as cold as WISE 085510.83–071442.5, with T eff ≲ 300 K, however the F150W – F480M color is significantly bluer, possibly suggesting the presence of water clouds. Astrometry is measured at the JWST epoch for the sample which is consistent with parallax and proper motion values reported by J. D. Kirkpatrick et al. and F. Marocco et al.

Eccentric giant planets are predicted to have acquired their eccentricity through two major mechanisms: the Kozai-Lidov effect or planet-planet scattering, but it is normally difficult to separate the two mechanisms and determine the true eccentricity origin for a given system. In this work, we focus on a sample of 92 transiting, long-period giant planets (TLGs) as part of an eccentricity distribution study for this planet population in order to understand their eccentricity origin. Using archival high-contrast imaging observations, public stellar catalogs, precise Gaia astrometry, and the NASA Exoplanet Archive data base, we explored the eccentricity distribution correlation with different planet and host-star properties of our sample. We also homogeneously characterized the basic stellar properties for all 86 host-stars in our sample, including stellar age and metallicity. We found a correlation between eccentricity and stellar metallicity, where lower-metallicity stars ([Fe/H] $\le$ 0.1) did not host any planets beyond $e > 0.4$, while higher-metallicity stars hosted planets across the entire eccentricity range. Interestingly, we found no correlation between the eccentricity distribution and the presence of stellar companions, indicating that planet-planet scattering is likely a more dominant mechanism than the Kozai-Lidov effect for TLGs. This is further supported by an anticorrelation trend found between planet multiplicity and eccentricity, as well as a lack of strong tidal dissipation effects for planets in our sample, which favour planet-planet scattering scenarios for the eccentricity origin.

The population of giant planets on wide orbits around low-mass M dwarf stars is poorly understood, but the unprecedented sensitivity of JWST NIRCam coronagraphic imaging now provides direct access to planets significantly less massive than Jupiter beyond 10 au around the closest, youngest M dwarfs. We present the design, observations, and results of JWST Guaranteed Time Observation Program 1184, a Cycle 1 NIRCam coronagraphic imaging survey of nine very nearby and young low-mass stars at 3–5 μ m wavelengths. In the F356W and F444W filters, we achieve survey median 5 σ contrasts deeper than 10 ^−5 at a separation of 1″, corresponding to 0.20 M _Jup in F444W and 1.30 M _Jup in F356W at planet–star separations of 10 au. Our results include 3–5 μ m debris disk detections and the identification of many extended and point-like sources in the final postprocessed images. In particular, we have identified a marginal point-source candidate having flux and color limits consistent with model predictions for a young sub-Jupiter-mass exoplanet. Under the assumption that the candidate is not confirmed, we place the first direct-imaging occurrence constraints on M dwarf wide-orbit (semimajor axes of 10–100 au), sub-Jupiter-mass exoplanets (0.3–1 M _Jup ). We find frequency limits of <0.10 and <0.16 objects per star with 1 σ and 3 σ confidence, respectively. This survey showcases the unprecedented capabilities of JWST NIRCam coronagraphic imaging when targeting young, low-mass stars and acts as a precursor to broader surveys to place deep statistical constraints on wide-orbit, sub-Jupiter-mass planets around M dwarfs.

High-contrast observations with JWST can reveal key composition and vertical mixing dependent absorption features in the spectra of directly imaged planets across the 3–5 μ m wavelength range. We present novel coronagraphic images of the HR 8799 and 51 Eri planetary systems using the NIRCam Long Wavelength Bar in an offset “narrow” position. These observations have revealed the four known gas giant planets encircling HR 8799, even at spatial separations challenging for a 6.5 m telescope in the mid-infrared, including the first ever detection of HR 8799 e at 4.6 μ m. The chosen filters constrain the strength of CO, CH 4 , and CO 2 absorption in each planet’s photosphere. The planets display a diversity of 3–5 μ m colors that could be due to differences in composition and ultimately be used to trace their formation history. They also show stronger CO 2 absorption than expected from solar metallicity models, indicating that they are metal enriched. We detected 51 Eri b at 4.1 μ m and not at longer wavelengths, which, given the planet’s temperature, is indicative of out-of-equilibrium carbon chemistry and an enhanced metallicity. Updated orbits fit to the new measurement of 51 Eri b validate previous studies that find a preference for high eccentricities ( e = 0.5 7 − 0.09 + 0.03 ), which likely indicates some dynamical processing in the system’s past. These results present an exciting opportunity to model the atmospheres and formation histories of these planets in more detail in the near future, and are complementary to future higher-resolution, continuum-subtracted JWST spectroscopy.

The Palomar Radial Velocity Instrument (PARVI) is a J & H band, high resolution (R similar to 80,000) spectrograph on the Hale 5.08-m telescope at Palomar Observatory. PARVI is a stabilized, single-mode fiber-fed spectrometer designed to search for small rocky planets in the habitable zones of late-type stars. PARVI is one of the first radial velocity (RV) instruments to employ single-mode fibers (SMF) instead of the more common multi-mode fibers (MMF). SMFs provide a number of advantages over MMFs. In particular, they only allow one spatial mode of light to propagate, resulting in a time-invariant, near-Gaussian output beam that eliminates speckle noise present in MMFs. A challenge with SMFs is that the single spatial mode is composed of two polarization states (PS) and the output PS is completely decoupled from the input PS. During the commissioning of PARVI, we discovered a source of polarization noise that manifested as a time-dependent, wavelength-dependent, PSF displacement responsible for RV errors on the order of 10 ms-1 that we call the accordion effect. We set up a warm testbed to test the polarization response of the PARVI optics and determined the cross-dispersing prism and variable PS of injected light were responsible for the polarization noise. We used raytracing software to simulate birefringence in the prism and found it to be consistent with the observed effect. We designed a number of tests with the PARVI spectrometer operating cold and under vacuum to evaluate how modifications to the prism impacted the effect. After mitigating stress-induced birefringence in the prism and installing fiber polarization scramblers before light is injected into the spectrograph, we are able to demonstrate an instrument RV precision of <1 ms(-1). (c) 2024 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI:10.1117/1.JATIS.11.1.015001]

We present a near-complete spectral energy distribution (SED) for an extrasolar world: the T8 brown dwarf 2MASS J04151954−0935066. Spanning from optical to mid-infrared (0.7–20.4 μ m) wavelengths, the SED for this substellar atmosphere is constructed from new James Webb Space Telescope (JWST) NIRSpec G395H ( R ∼ 2700) and Magellan Folded-port InfraRed Echellete (FIRE) echelle ( R ∼ 8000) near-infrared spectra, along with MIRI mid-infrared photometry complemented by spectra from Keck I, Infrared Telescope Facility, Magellan, AKARI, Spitzer, and photometry from various surveys and missions. The NIRSpec G395H spectrum reveals strong molecular absorptions from NH _3 , CH _4 , H _2 S, CO _2 , and H _2 O at approximately 3.00, 3.35, 3.95, 4.25, and 5.00 μ m, respectively, along with the presence of a CO absorption feature detected mainly at ∼4.6 μ m. We detect no absorption of near-infrared K i doublets in the R ∼ 8000 FIRE spectra. In the mid-infrared Infrared Spectrograph spectrum, we tentatively identify a new CO _2 feature at 14–16 μ m. The comprehensive SED allows us to empirically constrain bolometric luminosity, effective temperature, mass, and radius. Additionally, we demonstrate that the NIRSpec G395H resolution, the highest allowable by JWST, enables a precise radial velocity measurement of 47.1 ± 1.8 km s ^−1 for the object, in agreement with previous measurements.

We present the first brown dwarf spectral binary characterized with JWST: WISE J014656.66+423410.0, the coldest blended-light brown dwarf binary straddling the T/Y transition. We obtained a moderate resolution ( R ∼ 2700) G395H spectrum of this unresolved binary with JWST/NIRSpec and we fit it to late T and Y dwarf spectra from JWST/NIRSpec, and model spectra of comparable temperatures, both as individual spectra and pairs mimicking an unresolved binary system. We find that this tightly separated binary is likely composed of two unequal-brightness sources with a magnitude difference of 0.50 ± 0.08 mag in IRAC [4.5] and a secondary 1.01 ± 0.13 mag redder than the primary in [3.6]–[4.5]. Despite the large color difference between the best-fit primary and secondary, their temperature difference is only 92 ± 23 K, a feature reminiscing of the L/T transition. Carbon disequilibrium chemistry strongly shapes the mid-infrared spectra of these sources, as a complex function of the metallicity and surface gravity. While a larger library of JWST/NIRSpec spectra is needed to conclusively examine the peculiarities of blended-light sources, this spectral binary is a crucial pathfinder to both understand the spectral features of planetary-mass atmospheres and detect binarity in unresolved, moderate-resolution spectra of the coldest brown dwarfs.

The most prominent of the IRAS debris disk systems, alpha Lyrae (Vega), at a distance of 7.7 pc, has been observed by both the NIRCam and MIRI instruments on the James Webb Space Telescope. This paper describes NIRCam coronagraphic observations, which have achieved F444W contrast levels of 3 x 10(-7) at 1 '' (7.7 au), 1 x 10(-7) at 2 '' (15 au), and a few x 10(-8) beyond 5 '' (38 au), corresponding to masses of <3, 2, and 0.5 M J for a system age of 700 Myr. Two F444W objects are identified in the outer MIRI debris disk, around 48 au. One of these is detected by MIRI and appears to be extended with a spectral energy distribution similar to those of distant extragalactic sources. The second one also appears extended in the NIRCam data suggestive of an extragalactic nature. The NIRCam limits within the inner disk (1 ''-10 '') correspond to model-dependent masses of 2-3 M-J. K. Y. L. Su et al. argue that planets larger than 0.3 M(J )would disrupt the smooth disk structure seen at MIRI wavelengths. Eight additional objects are found within 60 '' of Vega, but none have astrometric properties or colors consistent with planet candidates. These observations reach a level consistent with expected Jeans mass limits. Deeper observations achieving contrast levels < 10(-8) outside of similar to 4 '' and reaching masses below that of Saturn are possible, but may not reveal a large population of new objects.

The latest generation of high-resolution spectrograph instruments on 10m-class telescopes continue to pursue challenging science cases. Consequently, ever more precise calibration methods are necessary to enable trail-blazing science methodology. We present the High-resolution Infrared SPectrograph for Exoplanet Characterization (HISPEC) Calibration Unit (CAL), designed to facilitate challenging science cases such as Doppler imaging of exoplanet atmospheres, precision radial velocity, and high-contrast high-resolution spectroscopy of nearby exoplanets. CAL builds upon the heritage from the pathfinder instrument Keck Planet Imager and Characterizer (KPIC) and utilizes four near-infrared (NIR) light sources encoded with wavelength information that are coupled into single-mode fibers. They can be used synchronously during science observations or asynchronously during daytime calibrations. A hollow cathode lamp (HCL) and a series of gas absorption cells provide absolute calibration from 0.98 {\mu}m to 2.5 {\mu}m. A laser frequency comb (LFC) provides stable, time-independent wavelength information during observation and CAL implements a lower finesse astro-etalon as a backup for the LFC. Design lessons from instrumentation like HISPEC will serve to inform the requirements for similar instruments for the ELTs in the future.

The launch of the James Webb Space Telescope (JWST) marks a pivotal moment for precise atmospheric characterization of Y dwarfs, the coldest brown dwarf spectral type. In this study, we leverage moderate spectral resolution observations (R $\sim$ 2700) with the G395H grating of the Near-Infrared Spectrograph (NIRSpec) onboard of JWST to characterize the nearby (9.9 pc) Y dwarf WISEPA J182831.08+265037.8 (WISE 1828). With the NIRSpec G395H 2.88-5.12 $\mathrm{\mu}$m spectrum, we measure the abundances of CO, CO$_2$, CH$_4$, H$_2$S, NH$_3$, and H$_2$O, which are the major carbon, nitrogen, oxygen, and sulfur bearing species in the atmosphere. Based on the retrieved volume mixing ratios with the atmospheric retrieval framework CHIMERA, we report that the C/O ratio is $0.45 \pm 0.01$, close to the solar C/O value of 0.55, and the metallicity to be +0.30 $\pm$ 0.02 dex. Comparison between the retrieval results with the forward modeling results suggests that the model bias for C/O and metallicity could be as high as 0.03 and 0.97 dex respectively. We also report a lower limit of the $^{12}$CO/$^{13}$CO ratio of $>40 $, being consistent with the nominal solar value of 90. Our results highlight the potential of JWST in measuring the C/O ratios down to percent-level precision and characterizing isotopologues of cold planetary atmospheres similar to WISE 1828.

Beyond our Solar System, aurorae have been inferred from radio observations of isolated brown dwarfs1,2. Within our Solar System, giant planets have auroral emission with signatures across the electromagnetic spectrum including infrared emission of H3+ and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features, but only null detections have been reported3. CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of approximately 482 K. Here we report James Webb Space Telescope observations of strong methane emission from W1935 at 3.326 μm. Atmospheric modelling leads us to conclude that a temperature inversion of approximately 300 K centred at 1-10 mbar replicates the feature. This represents an atmospheric temperature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and external dynamical processes cannot be ruled out. The best-fitting model rules out the contribution of H3+ emission, which is prominent in Solar System gas giants. However, this is consistent with rapid destruction of H3+ at the higher pressure where the W1935 emission originates4.

We present the analysis of the microlensing event OGLE-2015-BLG-0845, which was affected by both the microlensing parallax and xallarap effects. The former was detected via the simultaneous observations from the ground and Spitzer, and the latter was caused by the orbital motion of the source star in a relatively close binary. The combination of these two effects led to a mass measurement of the lens object, revealing a low-mass (0.14 ± 0.05 M_⊙) M-dwarf at the bulge distance (7.6 ± 1.0 kpc). The source binary consists of a late F-type subgiant and a K-type dwarf of ∼1.2 M_⊙ and ∼ 0.9 M_⊙, respectively, and the orbital period is 70 ± 10 days. OGLE-2015-BLG-0845 is the first single-lens event in which the lens mass is measured via the binarity of the source. Given the abundance of binary systems as potential microlensing sources, the xallarap effect may not be a rare phenomenon. Our work thus highlights the application of the xallarap effect in the mass determination of microlenses, and the same method can be used to identify isolated dark lenses.

In the pursuit of understanding the population of stellar remnants within the Milky Way, we analyze the sample of similar to 950 microlensing events observed by the Spitzer Space Telescope between 2014 and 2019. In this study we focus on a subsample of nine microlensing events, selected based on their long timescales, small microlensing parallaxes, and joint observations by the Gaia mission, to increase the probability that the chosen lenses are massive and the mass is measurable. Among the selected events we identify lensing black holes and neutron star candidates, with potential confirmation through forthcoming release of the Gaia time-series astrometry in 2026. Utilizing Bayesian analysis and Galactic models, along with the Gaia Data Release 3 proper-motion data, four good candidates for dark remnants were identified: OGLE-2016-BLG-0293, OGLE-2018-BLG-0483, OGLE-2018-BLG-0662, and OGLE-2015-BLG-0149, with lens masses of 3.0-1.3+1.8M circle dot , 4.7-2.1+3.2M circle dot , 3.15-0.64+0.66M circle dot and 1.40-0.55+0.75M circle dot , respectively. Notably, the first two candidates are expected to exhibit astrometric microlensing signals detectable by Gaia, offering the prospect of validating the lens masses. The methodologies developed in this work will be applied to the full Spitzer microlensing sample, populating and analyzing the timescale (t E) versus parallax (pi E) diagram to derive constraints on the population of lenses in general and massive remnants in particular.

We present observations of the T8 dwarf 2MASS 0415-0935 with JWST's NIRSpec spectrograph using the G395H grating ($\sim$ 2.87 - 5.14 $\mu$m). We perform the first atmospheric retrieval analysis at the maximum spectral resolution of NIRSpec (R$\sim$2700) and combine the spectrum with previous observations to study the 0.9-20 $\mu$m spectral energy distribution. We obtain precise constraints on chemical abundances ($\sim$0.02 dex) for a number of species which complicate our understanding of disequilibrium chemistry, particularly for CO$_{2}$ and PH$_{3}$. Furthermore, we measure a $^{12}$CO/$^{13}$CO ratio of $\sim 97^{+9}_{-8}$, making 2MASS 0415-0935 the coldest ($\sim 760$ K) substellar object outside of our solar system with a measured $^{12}$CO/$^{13}$CO ratio. This work shows promise for similar observations with JWST to provide precise abundances of major chemical species as well as isotopologues, allowing for new tests of our understanding of the formation and atmospheres of substellar objects.

The Transiting Exoplanet Survey Satellite (TESS) has discovered hundreds of new worlds, with TESS planet candidates now outnumbering the total number of confirmed planets from Kepler. Owing to differences in survey design, TESS continues to provide planets that are better suited for subsequent follow-up studies, including mass measurement through radial velocity (RV) observations, compared to Kepler targets. In this work, we present the TESS-Keck Survey’s (TKS) Mass Catalog: a uniform analysis of all TKS RV survey data that has resulted in mass constraints for 126 planets and candidate signals. This includes 58 mass measurements that have reached ≥5 σ precision. We confirm or validate 32 new planets from the TESS mission either by significant mass measurement (15) or statistical validation (17), and we find no evidence of likely false positives among our entire sample. This work also serves as a data release for all previously unpublished TKS survey data, including 9,204 RV measurements and associated activity indicators over our three-year survey. We took the opportunity to assess the performance of our survey and found that we achieved many of our goals, including measuring the mass of 38 small (<4 R ⊕ ) planets, nearly achieving the TESS mission’s basic science requirement. In addition, we evaluated the performance of the Automated Planet Finder as survey support and observed meaningful constraints on system parameters, due to its more uniform phase coverage. Finally, we compared our measured masses to those predicted by commonly used mass–radius relations and investigated evidence of systematic bias.

Ground-based Precision Radial Velocity (PRV) measurements are inevitably impeded by contamination from telluric absorption features, particularly in the infrared region. Thus, it is crucial to improve modeling of the telluric absorption features down to the spectral noise level. As part of the efforts towards improved PRV measurements, we have taken an existing atmospheric trace gas retrieval algorithm (GFIT) and have successfully adapted it to fit the telluric absorption features in stellar spectra down to the spectral noise level (typically similar to 1%). We have established a stellar spectral fitting processing pipeline, Stellar-GFIT, to analyze a series of stellar spectra observed by two spectrographs, PARVI (1.1-1.76 mu m) commissioned at the Palomar Observatory (Palomar Mountain, CA) and iSHELL (1-5 mu m) deployed on the IRTF (Mauna Kea, HI). For this, we have (1) implemented a Gaussian instrumental line shape function, (2) generated atmospheric models (consisting of temperature, pressure, and volume mixing ratios of all the known trace gases) for the particular observation sites and times, (3) employed the most up-to-date spectroscopic parameters in the target spectral regions, and finally (4) developed a series of spectral fitting intervals of similar to 60 cm-1 width, i.e., micro-windows, customized to the individual orders of each spectrograph. Stellar-GFIT is also capable of handling non-telluric features, such as transitions from a gas cell placed in the starlight beam and stellar features if a model spectrum template is available for the target star. We present spectrum fits from the observations of various target stars and discuss the performance and advantages of our novel approach. One of the major strengths of Stellar-GFIT is an ability to adjust the abundance of atmospheric trace gases simultaneously with determining the stellar doppler shift, mitigating any adverse impacts of short-timescale variations of water vapor.