NaI Doublet Research Articles

Transmission spectroscopy of MASCARA-1b with ESPRESSO: Challenges of overlapping orbital and Doppler tracks

Atmospheric studies at high spectral resolution have shown the presence of molecules, neutral and ionised metals, and hydrogen in the transmission spectrum of ultra-hot Jupiters, and have started to probe the dynamics of their atmospheres. We analyse the transmission spectrum of MASCARA-1b, one of the densest ultra-hot Jupiters orbiting a bright (V = 8.3) star. We focus on the CaII H&K, NaI doublet, LiI, Hα, and KI D1 spectral lines and on the cross-correlated FeI, Fe II, CaI, YI, VI, VII, CaH, and TiO lines. For those species that are not present in the stellar spectrum, no detections are reported, but we are able to measure upper limits with an excellent precision (~10 ppm for particular species) thanks to the signal-to-noise ratio (S/N) achieved with Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) observations. For those species that are present in the stellar spectrum and whose planet-occulted spectral lines induce spurious features in the planetary transmission spectrum, an accurate modelling of the Rossiter-McLaughlin effect (RM) and centre-to-limb variations (CLV) is necessary to recover possible atmospheric signals. In the case of MASCARA-1b, this is difficult due to the overlap between the radial velocities of the stellar surface regions occulted by MASCARA-1b and the orbital track along which the planet atmospheric signal is expected to be found. To try to disentangle a possible planetary signal, we compare our results with models of the RM and CLV effects, and estimate the uncertainties of our models depending on the different system parameters. Unfortunately, more precise measurements of the spin-orbit angle are necessary to better constrain the planet-occulted track and correct for the transit effects in the transmission spectrum with enough precision to be able to detect or discard possible planetary absorptions. Finally, we discuss the possibility that non-detections are related to the low absorption expected for a high surface gravity planet such as MASCARA-1b. Other techniques such as emission spectroscopy may be more useful for exploring their atmospheric composition.

Instability of the kinematic state in the atmosphere of the hypergiant ρ Cas outside outburst

Multiple observations of the yellow hypergiant ρ Cas obtained in 2007–2011 in a wide wavelength range with spectroscopic resolving power R ≥ 60 000 have enabled studies of features of its optical spectrum in detail and brought to light previously unknown characteristics of the star’s extended atmosphere. The radial velocity measured from symmetric absorption lines of metals varies with an amplitude of about ±7 km/s around the systemic velocity V sys = −47 km/s, due to low-amplitude pulsations of the atmospheric layers near the photosphere. At some times, a velocity gradient was observed in deep atmospheric layers of the star. A slight velocity stratification in the stellar atmosphere was detected for the first time, manifest as a difference of 3–4 km/s in the velocities measured from absorption lines of neutral metals and of ions. The long-wavelength components of split absorption lines of BaII, SrII, TiII, and other strong lines with low excitation potentials for their lower levels are distorted by nearby emission lines. It is suggested that the short-wavelength components, whose locations correspond to the narrow velocity range V r (blue) from approximately −60 to −70 km/s, are formed in a circumstellar envelope; one component of the D NaI doublet and the emission components of the FeII 6369.46 and 6432.68 Å ions are also formed there.

Towards precise ages and masses of Free Floating Planetary Mass Brown Dwarfs

Measurement of the substellar initial mass function (IMF) in very young clusters is hampered by the possibility of the age spread of cluster members. This is particularly serious for candidate planetary mass objects (PMOs), which have a very similar location to older and more massive brown dwarfs on the Hertzsprung-Russell Diagram (HRD). This degeneracy can be lifted by the measurement of gravity-sensitive spectral features. To this end we have obtained medium resolution (R~5000) Near-infrared Integral Field Spectrometer (NIFS) K band spectra of a sample of late M- / early L-type dwarfs. The sample comprises old field dwarfs and very young brown dwarfs in the Taurus association and in the Sigma Orionis cluster. We demonstrate a positive correlation between the strengths of the 2.21micron NaI doublet and the objects' ages. We demonstrate a further correlation between these objects' ages and the shape of their K band spectra. We have quantified this correlation in the form of a new index, the H2(K) index. This index appears to be more gravity-sensitive than the NaI doublet and has the advantage that it can be computed for spectra where gravity-sensitive spectral lines are unresolved, while it is also more sensitive to surface gravity at very young ages (<10 Myr) than the triangular H band peak. Both correlations differentiate young objects from field dwarfs, while the H2(K) index can distinguish, at least statistically, populations of ~1 Myr objects from populations of ~10 Myr objects. We applied the H2(K) index to NIFS data for one Orion nebula cluster (ONC) PMO and to previously published low resolution spectra for several other ONC PMOs where the 2.21micron NaI doublet was unresolved and concluded that the average age of the PMOs is ~1 Myr.

The spectral type of CHS 7797 - an intriguing very low mass periodic variable in the Orion Nebula Cluster

We present the spectroscopic characterization of the unusual high-amplitude very low mass pre-main-sequence periodic variable CHS7797. This study is based on optical medium-resolution (R=2200) spectroscopy in the 6450-8600 A range, carried out with GMOS-GEMINI-S in March 2011. Observations of CHS7797 have been carried out at two distinct phases of the 17.8d period, namely at maximum and four days before maximum. Four different spectral indices were used for the spectral classification at these two phases, all of them well-suited for spectral classification of young and obscured late M dwarfs. In addition, the gravity-sensitive NaI (8183/8195 A) and KI (7665/7699 A) doublet lines were used to confirm the young age of CHS7797. From the spectrum obtained at maximum light we derived a spectral type (SpT) of M6.05, while for the spectrum taken four days before maximum the derived SpT is M5.75. The derived SpTs confirm that CHS7797 has a mass in the stellar-substellar boundary mass range. In addition, the small differences in the derived SpTs at the two observed phases may provide indirect hints that CHS7797 is a binary system of similar mass components surrounded by a tilted circumbinary disk, a system similar to KH15D.

Spectral characteristics of the femtosecond laser plasma induced on the surface of sea water

Characteristic decay times of continuum and emission doublet intensities (MgII 279.6 and 280.3, CaII 393.4 and 396.8, NaI 589 and 589.6 nm) are presented. Measurements were carried out for plasma induced by a 42-fs laser pulse within a time interval of 0–85 ns. It is shown that the NaI doublet intensity is described by a monoexponential dependence throughout the whole observation time interval. Using the triple recombination coefficient, the electron density has been estimated to vary from 3.0 × 1016 to 2.4 × 1015 cm−3. The validity of the local thermodynamic equilibrium criterion and the dependence of the line intensity-to-background ratio on the delay time are studied.

The stellar initial mass function in red-sequence galaxies: 1-μm spectroscopy of Coma cluster galaxies with Subaru/FMOS

To investigate possible variations in the stellar initial mass function (IMF) in red-sequence galaxies, we have obtained infrared spectroscopy with Subaru/FMOS for a sample of 92 red-sequence galaxies in the Coma cluster. Velocity dispersions, ages and element abundances for these galaxies have been previously determined from optical data. By stacking the FMOS spectra in the rest frame, removing sky-subtraction residuals and other artefacts fixed in the observed frame, we derive composite spectra in the 9600-10500 Angstrom range for galaxies grouped according to their velocity dispersion or Mg/Fe ratio. We measure the Wing-Ford band of FeH and a new index centred on a CaI line at 10345 Angstrom; these features are strong in cool dwarf stars, and hence reflect the form of the IMF at low mass (<0.5M_sun) The CaI line, unlike the Wing-Ford band and other `classical' IMF indicators (NaI doublet, CaII triplet), is unaffected by the abundance of sodium. We compare the measured indices against predictions from spectral synthesis models matched to the element abundances estimated from the optical data. Binning galaxies by velocity dispersion, we find that both the Wing-Ford and CaI index measurements are best reproduced by models with the Salpeter IMF. There is no clear evidence for an increase in dwarf-star content with velocity dispersion. Binning the observed galaxies instead by Mg/Fe ratio, the behaviour of both indices implies a trend of IMF from Chabrier-like, at abundance ratios close to solar, to Salpeter or heavier for highly alpha-enhanced populations. At face value, this suggests that the IMF depends on the mode of star formation, with intense rapid star-bursts generating a larger population of low-mass stars.

The upper atmosphere of the exoplanet HD 209458 b revealed by the sodium D lines

A complete reassessment of the HST observations of the transits of the extrasolar planet HD209458b has provided a transmission spectrum of the atmosphere over a wide range of wavelengths. Analysis of the NaI absorption line profile has already shown that the sodium abundance has to drop by at least a factor of ten above a critical altitude. Here we analyze the profile in the deep core of the NaI doublet line from HST and high-resolution ground-based spectra to further constrain the vertical structure of the HD209458b atmosphere. With a wavelength-dependent cross section that spans more than 5 orders of magnitude, we use the absorption signature of the NaI doublet as an atmospheric probe. The NaI transmission features are shown to sample the atmosphere of HD209458b over an altitude range of more than 6500km, corresponding to a pressure range of 14 scale heights spanning 1 millibar to 1e-9 bar pressures. By comparing the observations with a multi-layer model in which temperature is a free parameter at the resolution of the atmospheric scale height, we constrain the temperature vertical profile and variations in the Na abundance in the upper part of the atmosphere of HD209458b. We find a rise in temperature above the drop in sodium abundance at the 3mbar level. We also identify an isothermal atmospheric layer at 1500+/-100K spanning almost 6 scale heights in altitude, from 1e-5 to 1e-7 bar. Above this layer, the temperature rises again to 2500(+1500/-1000)K at 1e-9 bar, indicating the presence of a thermosphere. The resulting temperature-pressure (T-P) profile agrees with the Na condensation scenario at the 3 mbar level, with a possible signature of sodium ionization at higher altitudes, near the 3e-5 bar level. Our T-P profile is found to be in good agreement with the profiles obtained with aeronomical models including hydrodynamic escape.

Spectroscopic characterization of 78 DENIS ultracool dwarf candidates in the solar neighborhood and the Upper Scorpii OB association

Aims: Low-resolution optical spectroscopic observations for 78 very low-mass star and brown dwarf candidates that have been photometrically selected using the DENIS survey point source catalogue. Methods: Spectral types are derived for them using measurements of the PC3 index. They range from M6 to L4. H_alpha emission and NaI subordinate doublet (818.3 nm and 819.9 nm) equivalent widths are measured in the spectra. Spectroscopic indices of TiO, VO, CrH and FeH molecular features are also reported. Results: A rule-of-thumb criterion to select young very low-mass objects using the NaI doublet equivalent width is given. It is used to confirm seven new members of the Upper Sco OB association and two new members of the R Cr-A star-forming region. Four of our field objects are also classified as very young, but are not members of any known nearby young association. The frequency of lower-gravity young objects in our field ultracool sample is 8.5%. Our results provide the first spectroscopic classification for 38 ultracool dwarfs in the solar vicinity with spectrophotometric distances in the range 17 pc to 65 pc (3 of them are new L dwarfs within 20 pc).

New 3D gas density maps of NaI and CaII interstellar absorption within 300 pc

We present new high resolution (R>50,000) absorption measurements of the NaI doublet (5889 - 5895A) along 482 nearby sight-lines, in addition to 807 new measurements of the CaII K (3933A) absorption line. We have combined these new data with previously reported measurements to produce a catalog of absorptions towards a total of 1857 early-type stars located within 800pc of the Sun. Using these data we have determined the approximate 3-dimensional spatial distribution of neutral and partly ionized interstellar gasdensity within a distance-cube of 300pc from the Sun. All newly recorded spectra were analyzed by means of a multi-component line profile-fitting program, in most cases using simultaneous fits to the line doublets. Normalized absorption profiles were fitted by varying the velocity, doppler width and column density for all intervening interstellar clouds. The resulting total column densities were then used in conjunction with the Hipparcos distances of the target stars to construct inversion maps of the 3-D spatial density distribution of the NaI and CaII bearing gas. A plot of the equivalent width of NaI versus distance reveals a wall of neutral gas at ~80pc that can be associated with the boundary wall to the central rarefied Local Cavity region. In contrast, a similar plot for the equivalent width of CaII shows no sharply increasing absorption at 80pc, but instead we observe a slowly increasing value of CaII equivalent width with increasing sight-line distance sampled.

Observation and modelling of main sequence star chromospheres

Aims. We report on high resolution observations of chromospheric lines for M and K dwarfs. Methods. We observed up to 13 spectral lines per star: the Hα ,H β ,H � ,P a � ,P a 8, CaII H, CaII IR triplet, CaI 6572A, NaI D1/D2 and HeI D3 lines. We observed two dMe stars, one dM(e) star, 5 dM stars and 3 dK stars. Results. We observed a self-reversal in the emission core of the CaII H line for the brightest stars only, indicating a rather optically thick region of formation. We present original spectra of the NaI doublet and the CaII IR triplet for active dMe stars and less active dM stars. Core emission is detected in the Sodium lines and the CaII IR triplet lines for the most active M dwarf AU Mic. We investigate the difference spectra between active dMe stars and dM stars and show that these provide interesting new constraints for the NLTE-radiation transfer modelling of the chromospheres. In our sample, emission Hα profiles have a rather homogeneous FWHM of about 1.5 A. This, according to our previous modelling, can be interpreted as the signature of a rather constant temperature break in the chromosphere. We found that one of our targets (MCC 332) is a binary with a faint but active Hα emission component. – –

An IPHAS-based search for accreting very low-mass objects using VO tools

The main goal of this paper is to prove that accreting very low-mass stars and brown dwarfs can be identified in IPHAS, a Halpha emission survey of the northern Milky Way.Full exploitation of the IPHAS database and a future extension of it in the southern hemisphere will be useful to identify very low-mass accreting objects near and far well-known star forming regions. We have used Virtual Observatory tools to cross-match the IPHAS catalogue with the 2MASS catalogue. We defined photometric criteria to identify Halpha emission sources with near-infrared colours similar to known young very low-mass stars and brown dwarfs. 4000 candidates were identified that met our criteria over an area of 1600 square degrees. We present low-resolution optical spectra of 113 candidates. Spectral types have been derived for the 33 candidates that have spectroscopically confirmed Halpha emission, negligible reddening and M spectral class. We have also measured Halpha emission and investigated the NaI doublet (818.3 nm, 819.5 nm) in these 33 objects. We confirm that 33 IPHAS candidates have strong Halpha indicative of disk accretion for their spectral type. 23 of them have spectral class M4 or later, of which 10 have classes in the range M5.5-M7.0 and thus could be very young brown dwarfs. Also many objects have weak NaI doublet, an indication of low surface gravity.We conclude that IPHAS provides a very valuable database to identify accreting very low-mass stars and brown dwarfs, and that Virtual Observatory tools provide an efficient method for identifying these objects over large areas of the sky. Based on our success rate of 23 Halpha emission objects with spectral type in the range M4-M7 out of 113 candidates with spectroscopic follow-up, we estimate that there could be hundreds of such objects in the full IPHAS survey.

Gas Absorption Detected from the Edge-on Debris Disk Surrounding HD 32297

Near-infrared and optical imaging of HD32297 indicate that it has an edge-on debris disk, similar to beta Pic. I present high resolution optical spectra of the NaI doublet toward HD32297 and stars in close angular proximity. A circumstellar absorption component is clearly observed toward HD32297 at the stellar radial velocity, which is not observed toward any of its neighbors, including the nearest only 0.9 arcmin away. An interstellar component is detected in all stars >90 pc, including HD32297, likely due to the interstellar material at the boundary of the Local Bubble. Radial velocity measurements of the nearest neighbors, BD+07 777s and BD+07 778, indicate that they are unlikely to be physically associated with HD32297. The measured circumstellar column density around HD32997, log N(NaI) ~ 11.4, is the strongest NaI absorption measured toward any nearby main sequence debris disk, even the prototypical edge-on debris disk, beta Pic. Assuming that the morphology and abundances of the gas component around HD32297 are similar to beta Pic, I estimate an upper limit to the gas mass in the circumstellar disk surrounding HD32297 of ~0.3 M_Earth.

A non-main-sequence secondary in SY Cancri

Simultaneous spectroscopic and photometric observations of the Z Cam type dwarf nova SY Cancri were used to obtain absolute flux calibrations. A comparison of the photometric calibration with a wide-slit spectrophotometric calibration showed that either method is equally satisfactory. A radial velocity study of the secondary star, made using the far-red Nai doublet, yielded a semi-amplitude of K2= 127 ± 23 km s−1. Taking the published value of 86 ± 9 km s−1 for K1 gives a mass ratio of q=M2/M1= 0.68 ± 0.14; this is very different from the value of 1.13 ± 0.35 quoted in the literature. Using the new lower mass ratio, and constraining the mass of the white dwarf to be within reasonable limits, then leads to a mass for the secondary star that is substantially less than would be expected for its orbital period if it satisfied a main-sequence mass–radius relationship. We find a spectral type of M0 that is consistent with that expected for a main-sequence star of the low mass we have found. However, in order to fill its Roche lobe, the secondary must be significantly larger than a main-sequence star of that mass and spectral type. The secondary is definitely not a normal main-sequence star.

Contamination and exclusion in theσOrionis young group

We present radial velocities for 38 low-mass candidate members of the sigma Orionis young group. We have measured their radial velocities by cross-correlation of high resolution (R~6000) AF2/WYFFOS spectra of the gravity sensitive NaI doublet at 8183, 8195Angstroms. The total sample contained 117 objects of which 54 have sufficient signal-to-noise to detect NaI at an equivalent width of 3Angstroms, however we only detect NaI in 38 of these. This implies that very low-mass members of this young group display weaker NaI absorption than similarly aged objects in the Upper Scorpius OB association. We develop a technique to assess membership using radial velocities with a range of uncertainties that does not bias the selection when large uncertainties are present. The resulting membership probabilities are used to assess the issue of exclusion in photometric selections, and we find that very few members are likely to be excluded by such techniques. We also assess the level of contamination in the expected pre-main sequence region of colour-magnitude space brighter than I = 17. We find that contamination by non-members in the expected PMS region of the colour-magnitude diagram is small. We conclude that although radial velocity alone is insufficient to confirm membership, high signal-to-noise observations of the NaI doublet provide the opportunity to use the strength of NaI absorption in concert with radial velocities to asses membership down to the lowest masses, where Lithium absorption no longer distinguishes youth.

Near-IR spectra of ISOGAL sources in the inner Galactic Bulge

In this work we present near-IR spectra (HK-band) of a sample of 107 sources with mid-IR excesses at 7 and 15 $\rm \mu$m detected during the ISOGAL survey. Making use of the DENIS interstellar extinction map from Schultheis et al. (1999) we derive luminosities and find that the $\rm M_{bol}$ vs.~$\rm ^{12}CO$ and $\rm M_{bol} vs. H_{2}O$ diagrams are powerful tools for identifying supergiants, AGB stars, giants and young stellar objects. The majority of our sample are AGB stars (~ 80%) while we find four good supergiant candidates, nine young stellar objects and 12 RGB candidates. We have used the most recent $\rm K_{0}-[15]$ relation by Jeong et al. (2002) based on recent theoretical modeling of dust formation of AGB stars to determine mass-loss rates. However, the uncertainties in the mass-loss rates are rather large. The mass-loss rates of the supergiants are comparable with those in the solar neighbourhood while the long-period Variables cover a mass-loss range from $\rm -5 < log \dot{\it{M}} < -7$. The red giant candidateslie at the lower end of the mass-loss rate range between $\rm -6.5 < log \dot{{\it{M}}} < -9$. We used the equivalent width of the CO bandhead at 2.3 $\rm \mu m$, the NaI doublet and the CaI triplet to estimate metallicities using the relation by Ram\'{\i}rez et al. (\cite{Ramirez2000}). The metallicity distribution of the ISOGAL objects shows a mean [Fe/H] $\sim$ -0.25 dex with a dispersion of $\rm \pm 0.40 dex$ which is in agreement with the values of Ram\'{i}rez et al. (\cite{Ramirez2000}) for Galactic Bulge fields between $\rm b = -4^{o}$ and $\rm b = -1.3^{o}$. A comparison with the solar neighbourhood sample of Lan\c{c}on & Wood (LW) shows that our sample is ~ 0.5 dex more metal-rich on average.

Spectroscopy of New Substellar Candidates in the Pleiades: Toward a Spectral Sequence for Young Brown Dwarfs

view Abstract Citations (226) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy of New Substellar Candidates in the Pleiades: Toward a Spectral Sequence for Young Brown Dwarfs Martin, Eduardo L. ; Rebolo, Rafael ; Zapatero-Osorio, Maria Rosa Abstract We present optical and near-infrared spectroscopy (600-1000 nm) of eight faint (I > 18) very red (R - I > 2.2) objects discovered in a recent deep CCD survey of the Pleiades cluster by ZapateroOsorio, Rebolo, & Martin. We compare them with reliable cluster members like PP1 15 and Teide 1, and with several field very late type dwarfs (M4-M9.5), which were observed with similar instrumental configurations. Using pseudocontinuum ratios, we classify the new substellar candidates in a spectral sequence defined with reference to field stars of known spectral types. We also reclassify PP1 15 and Teide 1 in a self- consistent way. The likelihood of membership for the new candidates is assessed via the study of their photospheric features, Ha emission, radial velocity, and consistency of their spectral types and I-band magnitudes with known cluster members. Four of the new substellar candidates are as late or later than PP1 15 (M6.5), but only one, namely, Calar 3 (M8), clearly meets all our membership criteria. It is indeed an object very similar to the brown dwarf Teide 1. Out of the eight new substellar candidates, our "cautious" membership analysis leaves only Calar 3 as a Pleiades brown dwarf with a high level of confidence. This object, together with Teide 1, allows one to compare the spectroscopic characteristics of Pleiades brown dwarfs with those of old very cool dwarfs. The overall spectral properties are similar, but there are slight differences in the NaI doublet (818.3 nm, 819.5 nm), VO molecular band (740 nm), and some spectral ratios, which are probably related to lower surface gravity in the young Pleiades brown dwarfs than in field stars. Finally, we propose a way of improving future CCD-based brown dwarf surveys by using narrowband near-IR pseudocontinuum filters. Publication: The Astrophysical Journal Pub Date: October 1996 DOI: 10.1086/177817 arXiv: arXiv:astro-ph/9604080 Bibcode: 1996ApJ...469..706M Keywords: GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL NAME: PLEIADES; STARS: LOW-MASS; BROWN DWARFS; Astrophysics E-Print: 25 pages, figures NOT included. Uuencoded and gzipped file. Full postscript (text and figures) available at http://www.iac.es/home.html full text sources arXiv | ADS | data products SIMBAD (31)

The 8190 A sodium doublet in cataclysmic variables - I. The Quest

We have carried out a near-infrared spectroscopic survey of 65 cataclysmic variables aimed at detecting absorption features from the secondary star, especially the NaI doublet at λλ8183.3, 8194.8 Å. We have positively identified these lines in 16 cataclysmic variables of various types with periods from 3 to 9 hr. Many of these objects show other features indicative of a late-type star. We have observed the λ7773 Å OI triplet in 28 objects. This feature varies considerably from object to object and may be a useful indicator of the state of the disc. We have also detected emission lines of HeI (λλ7065, 7281 Å), HeII (λ8236 Å), OI (λ8446 Å), CaII (λ8498 Å) and a further emission feature to the red of λ8200 Å that may be associated with the Paschen series limit.

Relativistic Contributions to Energies of Highly Ionized Atoms

Historically, the first observation of a relativistic effect in atomic spectra was probably the discovery by Fraunhofer of the splitting of the Nai doublet in the solar spectrum. Thus theoretical understanding of these effects has long been important for interpreting astrophysical spectra, and it is especially important for the ultraviolet and X-ray spectra which form our subject today, for these often arise in highly ionized atoms. Because the relative importance of relativistic to non-relativistic terms is proportional to Z2, where Z is the nuclear charge, relativistic effects often play a major role in such atoms.