ABSTRACT Studying the properties of young planetary systems can shed light on how the dynamics and structure of planets evolve during their most formative years. Recent K2 observations of nearby ...young clusters (10-800 Myr) have facilitated the discovery of such planetary systems. Here we report the discovery of a Neptune-sized planet transiting an M4.5 dwarf (K2-25) in the Hyades cluster (650-800 Myr). The light curve shows a strong periodic signal at 1.88 days, which we attribute to spot coverage and rotation. We confirm that the planet host is a member of the Hyades by measuring the radial velocity of the system with the high-resolution near-infrared spectrograph Immersion Grating Infrared Spectrometer. This enables us to calculate a distance based on K2-25's kinematics and membership to the Hyades, which in turn provides a stellar radius and mass to 5%-10%, better than what is currently possible for most Kepler M dwarfs (12%-20%). We use the derived stellar density as a prior on fitting the K2 transit photometry, which provides weak constraints on eccentricity. Utilizing a combination of adaptive optics imaging and high-resolution spectra, we rule out the possibility that the signal is due to a bound or background eclipsing binary, confirming the transits' planetary origin. K2-25b has a radius ( R⊕) much larger than older Kepler planets with similar orbital periods (3.485 days) and host-star masses (0.29 M ). This suggests that close-in planets lose some of their atmospheres past the first few hundred million years. Additional transiting planets around the Hyades, Pleiades, and Praesepe clusters from K2 will help confirm whether this planet is atypical or representative of other close-in planets of similar age.
Abstract
We present a comparative study of the near-infrared (NIR) H
2
line emission from five regions near hot young stars: Sharpless 140, NGC 2023, IC 63, the Horsehead Nebula, and the Orion Bar. ...This emission originates in photodissociation or photon-dominated regions (PDRs), interfaces between photoionized and molecular gas near hot (O) stars or reflection nebulae illuminated by somewhat cooler (B) stars. In these environments, the dominant excitation mechanism for NIR emission lines originating from excited rotational-vibrational (rovibrational) levels of the ground electronic state is radiative or UV excitation (fluorescence), wherein absorption of far-UV photons pumps H
2
molecules into excited electronic states from which they decay into the upper levels of the NIR lines. Our sources span a range of UV radiation fields (
G
0
= 10
2
−10
5
) and gas densities (
n
H
= 10
4
−10
6
cm
−3
), enabling examination of how these properties affect the emergent spectrum. We obtained high-resolution (
R
≈ 45,000) spectra spanning 1.45–2.45
μ
m on the 2.7 m Harlan J. Smith Telescope at McDonald Observatory with the Immersion Grating INfrared Spectrometer (IGRINS), detecting up to over 170 transitions per source from excited vibrational states (
v
= 1–14). The populations of individual rovibrational levels derived from these data clearly confirm UV excitation. Among the five PDRs in our survey, the Orion Bar shows the greatest deviation of the populations and spectrum from pure UV excitation, while Sharpless 140 shows the least deviation. However, we find that all five PDRs exhibit at least some modification of the level populations relative to their values under pure UV excitation, a result we attribute to collisional effects.
We present a study of the excitation conditions and metallicity of ionized gas (Z
gas) in eight nearby barred and unbarred spiral galaxies from the VIRUS-P Exploration of Nearby Galaxies (VENGA) ...survey, which provides high spatial sampling and resolution (median ∼387 pc), large coverage from the bulge to outer disc, broad wavelength range (3600–6800 Å), and medium spectral resolution (∼120 km s−1 at 5000 Å). Our results are: (1) We present high resolution gas excitation maps to differentiate between regions with excitation typical of Seyfert, LINER, or recent star formation. We find LINER-type excitation at large distances (3–10 kpc) from the centre, and associate this excitation with diffuse ionized gas (DIG). (2) After excluding spaxels dominated by Seyfert, LINER, or DIG, we produce maps with the best spatial resolution and sampling to date of the ionization parameter q, star formation rate, and Z
gas using common strong line diagnostics. We find that isolated barred and unbarred spirals exhibit similarly shallow Z
gas profiles from the inner kpc out to large radii (7–10 kpc or 0.5–1.0 R
25). This implies that if profiles had steeper gradients at earlier epochs, then the present-day bar is not the primary driver flattening gradients over time. This result contradicts earlier claims, but agrees with recent IFU studies. (3) The Z
gas gradients in our z ∼ 0 massive spirals are markedly shallower, by ∼0.2 dex kpc−1, than published gradients for lensed lower mass galaxies at z ∼ 1.5–2.0. Cosmologically motivated hydrodynamical simulations best match this inferred evolution, but the match is sensitive to adopted stellar feedback prescriptions.
The cosmic origin of fluorine is still not well constrained. Several nucleosynthetic channels at different phases of stellar evolution have been suggested, but these must be constrained by ...observations. For this, the fluorine abundance trend with metallicity spanning a wide range is required. Our aim is to determine stellar abundances of fluorine for . We determine the abundances from HF lines in infrared K-band spectra ( ) of cool giants, observed with the IGRINS and Phoenix high-resolution spectrographs. We derive accurate stellar parameters for all our observed K giants, which is important as the HF lines are very temperature-sensitive. We find that F/Fe is flat as a function of metallicity at F/Fe∼0, but increases as the metallicity increases. The fluorine slope shows a clear secondary behavior in this metallicity range. We also find that the F/Ce ratio is relatively flat for , and that for two metal-poor ( ), s-process element-enhanced giants, we do not detect an elevated fluorine abundance. We interpret all of these observational constraints as indications that several major processes are at play for the cosmic budget of fluorine over time: from those in massive stars at low metallicities, through the asymptotic giant branch star contribution at , to processes with increasing yields with metallicity at supersolar metallicities. The origins of the latter, and whether or not Wolf-Rayet stars and/or novae could contribute at supersolar metallicities, is currently not known. To quantify these observational results, theoretical modeling is required. More observations in the metal-poor region are required to clarify the processes there.
Abstract We report the first high-resolution, detailed abundances of 21 elements for giants in the Galactic bulge/bar within 1° of the Galactic plane, where high extinction has rendered such studies ...challenging. Our high-signal-to-noise-ratio and high-resolution, near-infrared spectra of seven M giants in the inner bulge, located at ( l , b ) = (0°, +1°), are observed using the IGRINS spectrograph. We report the first multichemical study of the inner Galactic bulge by investigating, relative to a robust new solar neighborhood sample, the abundance trends of 21 elements, including the relatively difficult to study heavy elements. The elements studied are: F, Mg, Si, S, Ca, Na, Al, K, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Ce, Nd, and Yb. We investigate bulge membership of all seven stars using distances and orbital simulations, and we find that the most metal-poor star may be a halo interloper. Our investigation also shows that the inner bulge as close as 1° north of the Galactic Center displays a similarity to the inner disk sequence, following the high- α /Fe envelope of the solar vicinity metal-rich population, though no firm conclusions for a different enrichment history are evident from this sample. We find a small fraction of metal-poor stars (Fe/H > −0.5), but most of our stars are mainly of supersolar metallicity. Fluorine is found to be enhanced at high metallicity compared to the solar neighborhood, but confirmation with a larger sample is required. We will apply this approach to explore the populations of the nuclear stellar disk and the nuclear star cluster.
ABSTRACT
We study the stellar populations and assembly of the nearby spiral galaxy NGC 2903’s bulge, bar, and outer disc using the VIRUS-P Exploration of Nearby Galaxies IFS survey. We observe NGC ...2903 with a spatial resolution of 185 pc using the Mitchell Spectrograph’s 4.25 arcsec fibres at the 2.7 Harlan J. Smith telescope. Bulge–bar–disc decomposition on the Two Micron All-Sky Survey (2MASS) Ks-band image of NGC 2903 shows that it has ∼6 per cent, 6 per cent, and 88 per cent, of its stellar mass in the bulge, bar, and outer disc, respectively, and its bulge has a low Sérsic index of ∼0.27, suggestive of a discy bulge. We perform stellar population synthesis and find that the outer disc has 46 per cent of its mass in stars >5 Gyr, 48 per cent in stars between 1 and 5 Gyr, and <10 per cent in younger stars. Its stellar bar has 65 per cent of its mass in ages 1–5 Gyr and has metallicities similar to the outer disc, suggestive of the evolutionary picture where the bar forms from disc material. Its bulge is mainly composed of old high-metallicity stars though it also has a small fraction of young stars. We find enhanced metallicity in the spiral arms and central region, tracing areas of high star formation as seen in the Hα map. These results are consistent with the idea that galaxies of low bulge-to-total mass ratio and low bulge Sérsic index like NGC 2903 has not had a recent major merger event, but has instead grown mostly through minor mergers and secular processes.
We identify Rbiv 1.5973 and Cdiv 1.7204 mum emission lines in high-resolution (R= 40,000) near-infrared spectra of the planetary nebulae (PNe) NGC 7027 and IC 5117, obtained with the Immersion ...GRating INfrared Spectrometer (IGRINS) on the 2.7 m telescope at McDonald Observatory. We also identify Gevi 2.1930 mum in NGC 7027. Alternate identifications for these features are ruled out based on the absence of other multiplet members and/or transitions with the same upper levels. Ge, Rb, and Cd can be enriched in PNe by s-process nucleosynthesis during the asymptotic giant branch stage of evolution. To determine ionic abundances, we calculate Rbiv collision strengths and use approximations for those of Cdiv and Gevi. Our identification of Rbiv 1.5973 mum is supported by the agreement between Rb super(3+)/H super(+) abundances found from this line and the 5759.55 A feature in NGC 7027. Elemental Rb, Cd, and Ge abundances are derived with ionization corrections based on similarities in ionization potential ranges between the detected ions and O and Ne ionization states. Our analysis indicates abundances 2-4 times solar for Rb and Cd in both nebulae. Ge is subsolar in NGC 7027, but its abundance is uncertain due to the large and uncertain ionization correction. The general consistency of the measured relative s-process enrichments with predictions from models appropriate for these PNe (2.0-2.5 M sub(middot in circle), Fe/H = -0.37) demonstrates the potential of using PN compositions to test s-process nucleosynthesis models.
We present a library of high-resolution (R λ/Δλ ∼ 45,000) and high signal-to-noise ratio (S/N ≥ 200) near-infrared spectra for stars of a wide range of spectral types and luminosity classes. The ...spectra were obtained with the Immersion GRating INfrared Spectrograph covering the full range of the H (1.496-1.780 m) and K (2.080-2.460 m) atmospheric windows. The targets were primarily selected for being MK standard stars covering a wide range of effective temperatures and surface gravities, with metallicities close to the solar value. Currently, the library includes flux-calibrated and telluric-absorption-corrected spectra of 84 stars, with prospects for expansion to provide denser coverage of the parametric space. Throughout the H and K atmospheric windows, we identified spectral lines that are sensitive to Teff or and defined corresponding spectral indices. We also provide their equivalent widths (EWs). For those indices, we derive empirical relations between the measured EWs and the stellar atmospheric parameters. Therefore, the derived empirical equations can be used to calculate the Teff and of a star without requiring stellar atmospheric models.
Abstract
We have used the Habitable Zone Planet Finder (HPF) to gather high-resolution, high signal-to-noise near-infrared spectra of 13 field red horizontal branch (RHB) stars, one open cluster ...giant, and one very metal-poor halo red giant. The HPF spectra cover the 0.81–1.28
μ
m wavelength range of the
zyJ
bands, partially filling the gap between the optical (0.4–1.0
μ
m) and infrared (1.5–2.4
μ
m) spectra already available for the program stars. We derive abundances of 17 species from LTE-based computations involving equivalent widths and spectrum syntheses, and estimate abundance corrections for the species that are most affected by departures from LTE in RHB stars. Generally good agreement is found between HPF-based metallicities and abundance ratios and those from the optical and infrared spectral regions. Light element transitions dominate the HPF spectra of these red giants, and HPF data can be used to derive abundances from species with poor or no representation in optical spectra (e.g., C
i
, P
i
, S
i
, K
i
). Attention is drawn to the HPF abundances in two field solar-metallicity RHB stars of special interest: one with an extreme carbon isotope ratio, and one with a rare, very large lithium content. The latter star is unique in our sample in exhibiting very strong He
i
10830 Å absorption. The abundances of the open cluster giant concur with those derived from other wavelength regions. Detections of C
i
and S
i
in HD 122563 are reported, yielding the lowest metallicity determination of S/Fe from more than one multiplet.
Abstract
We have identified two new near-infrared (NIR) emission lines in the spectra of planetary nebulae arising from heavy elements produced by neutron-capture reactions: Te
iii
2.1019
μ
m and Br
...v
1.6429
μ
m. Te
iii
was detected in both NGC 7027 and IC 418, while Br
v
was seen in NGC 7027. The observations were obtained with the medium-resolution spectrograph Espectrógrafo Multiobjeto Infra-Rojo (EMIR) on the 10.4 m Gran Telescopio Canarias at La Palma, and with the high-resolution Immersion GRating INfrared Spectrometer (IGRINS) on the 2.7 m Harlan J. Smith telescope at McDonald Observatory. New calculations of atomic data for these ions, specifically A-values and collision strengths, are presented and used to derive ionic abundances of Te
2+
and Br
4+
. We also derive ionic abundances of other neutron-capture elements detected in the NIR spectra, and estimate total elemental abundances of Se, Br, Kr, Rb, and Te after correcting for unobserved ions. Comparison of our derived enrichments to theoretical predictions from asymptotic giant branch (AGB) evolutionary models shows reasonable agreement for solar metallicity progenitor stars of ∼2–4
M
⊙
. The spectrally isolated Br
v
1.6429
μ
m line has advantages for determining nebular Br abundances over optical Br
iii
emission lines that can be blended with other features. Finally, measurements of Te are of special interest because this element lies beyond the first peak of the
s
-process, and thus provides new leverage on the abundance pattern of trans-iron species produced by AGB stars.
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