Equivalent Width Ratio Research Articles

Quantitative spectral classification of Galactic O stars

Our goal is to provide a quantification of several spectral classification criteria for O stars. We collect high-spectral resolution spectra of 105 Galactic O-type stars from various archives. We measured equivalent widths of classification lines. We defined average values of classification criteria for given spectral types and luminosity classes. We find that the ratio He I 4471 to He II 4542 well matches the published ratios for spectral types. We have quantified equivalent width ratios of helium and silicon lines among O8–O9.7 stars to refine spectral class typing in this spectral range. We present quantitative criteria to separate between luminosity class V, IV–III–II (grouped), and I among O3–O8.5 stars, mainly based on the strength of He II 4686. We find that these criteria also define very well the f, (f), and ((f)) classes for O3–O7.5 stars. Among O9–O9.7 stars we quantify the ratios of He II 4686 to He I 4713 and Si IV 4089 to He I 4026 for all luminosity classes. The tabulated values of the classification criteria should help classify any new O-type stars. The final step of the classification process should rely on a direct comparison to standard stars of the assigned spectral type or luminosity class.

The GAPS programme with HARPS-N at TNG

Context. The measurement of the orbital obliquity of hot Jupiters with different physical characteristics can provide clues to the mechanisms of migration and orbital evolution of this particular class of giant exoplanets. Aims. We aim to derive the degree of alignment between planetary orbit and stellar spin angular momentum vectors and look for possible links with other orbital and fundamental physical parameters of the star-planet system. We focus on the characterisation of five transiting planetary systems (HAT-P-3, HAT-P-12, HAT-P-22, WASP-39, and WASP-60) and the determination of their sky-projected planet orbital obliquity through the measurement of the Rossiter–McLaughlin effect. Methods. We used HARPS-N high-precision radial velocity measurements, gathered during transit events, to measure the Rossiter–McLaughlin effect in the target systems and determine the sky-projected angle between the planetary orbital plane and stellar equator. The characterisation of stellar atmospheric parameters was performed by exploiting the HARPS-N spectra, using line equivalent width ratios and spectral synthesis methods. Photometric parameters of the five transiting exoplanets were re-analysed through 17 new light curves, obtained with an array of medium-class telescopes, and other light curves from the literature. Survey-time-series photometric data were analysed for determining the rotation periods of the five stars and their spin inclination. Results. From the analysis of the Rossiter–McLaughlin effect we derived a sky-projected obliquity of λ = 21.2° ± 8.7°, λ = −54°−13°+41°, λ = −2.1° ± 3.0°, λ = 0° ± 11°, and λ = −129° ± 17° for HAT-P-3 b, HAT-P-12 b, HAT-P-22 b, WASP-39 b, and WASP-60 b, respectively. The latter value indicates that WASP-60 b is moving on a retrograde orbit. These values represent the first measurements of λ for the five exoplanetary systems under study. The stellar activity of HAT-P-22 indicates a rotation period of 28.7 ± 0.4 days, which allowed us to estimate the true misalignment angle of HAT-P-22 b, ψ = 24° ± 18°. The revision of the physical parameters of the five exoplanetary systems returned values that are fully compatible with those existing in the literature. The exception to this is the WASP-60 system, for which, based on higher quality spectroscopic and photometric data, we found a more massive and younger star and a larger and hotter planet.

An infrared photometric and spectroscopic study of post-AGB stars

We present here $Spitzer$ mid-infrared (IR) spectra and modeling of the spectral energy distribution (SED) of a selection of post-Asymptotic Giant Branch (PAGB) stars. The mid-IR spectra of majority of these sources showed spectral features such as polycyclic aromatic hydrocarbons (PAHs) and silicates in emission. Our results from SED modeling showed interesting trends of dependency between the photospheric and circumstellar parameters. A trend of dependency is also noticed between the ratios of equivalent widths (EWs) of various vibrational modes of PAHs and the photospheric temperature T$_{*}$ and model-derived stellar parameters for the sample stars. The PAGB mass loss rates derived from the SED models are found to be higher than those for the AGB stars. In a few objects, low and high excitation fine structure emission lines were identified, indicating their advanced stage of evolution. Further, IR vibration modes of fullerene (C$_{60}$) were detected for the first time in the PAGB star IRAS 21546+4721.

Developing Automated Spectral Analysis Tools for Interstellar Features Extractionto Support Construction of the 3D ISM Map

AbstractOne of the ways to obtain a detailed 3D ISM map is by gathering interstellar (IS) absorption data toward widely distributed background target stars at known distances (line-of-sight/LOS data). The radial and angular evolution of the LOS measurements allow the inference of the ISM spatial distribution. For a better spatial resolution, one needs a large number of the LOS data. It requires building fast tools to measure IS absorption. One of the tools is a global analysis that fit two different diffuse interstellar bands (DIBs) simultaneously. We derived the equivalent width (EW) ratio of the two DIBs recorded in each spectrum of target stars. The ratio variability can be used to study IS environmental conditions or to detect DIB family.

Updating quasar bolometric luminosity corrections – III. [O iii] bolometric corrections

We present quasar bolometric corrections using the [O III] $\lambda5007$ narrow emission line luminosity based on the detailed spectral energy distributions of 53 bright quasars at low to moderate redshift ($0.0345<z<1.0002$). We adopted two functional forms to calculate $L_{\textrm{iso}}$, the bolometric luminosity determined under the assumption of isotropy: $L_{\textrm{iso}}=A\,L_{[O\,III]}$ for comparison with the literature and log$(L_{iso})=B+C\,$log$(L_{[O\,III]})$, which better characterizes the data. We also explored whether "Eigenvector 1", which describes the range of quasar spectral properties and quantifies their diversity, introduces scatter into the $L_{[O\,III]}-L_{iso}$ relationship. We found that the [O III] bolometric correction can be significantly improved by adding a term including the equivalent width ratio $R_{Fe\,II}\equiv EW_{Fe\,II}/EW_{H\beta}$, which is an Eigenvector 1 indicator. Inclusion of $R_{Fe\,II}$ in predicting $L_{iso}$ is significant at nearly the $3\sigma$ level and reduces the scatter and systematic offset of the luminosity residuals. Typically, [O III] bolometric corrections are adopted for Type 2 sources where the quasar continuum is not observed and in these cases, $R_{Fe\,II}$ cannot be measured. We searched for an alternative measure of Eigenvector 1 that could be measured in the optical spectra of Type 2 sources but were unable to identify one. Thus, the main contribution of this work is to present an improved [O III] bolometric correction based on measured bolometric luminosities and highlight the Eigenvector 1 dependence of the correction in Type 1 sources.

Indicators of Stellar Mass in the Photometric H-band

Extensive infrared spectral surveys, such as the APOGEE survey in the H-band, are now being conducted, many targeting the Galactic Bulge and recording observations of primarily red giant stars. However, because stars of different masses converge to the red giant region, the masses of single red giant stars are poorly constrained. These surveys are now using spectral resolving powers that are high enough to measure the equivalent widths of individual spectral lines, which are mostly from molecular species. Because other observations can constrain or determine the star’s luminosity and radius, we have computed spherical stellar atmospheres for a fixed luminosity and radius but for a range of masses. We then computed the H-band flux spectrum for each model and searched for spectral lines that are sensitive to mass. Our synthetic spectra reveal many lines of CO that become weaker with increasing stellar mass. To explore this, we created a ratio of equivalent widths using a representative, unblended CO line and an unblended OH line that did not vary with mass. We found that this ratio varied about 30% over the mass range from to . We repeated the spectral analysis using spherical model stellar atmospheres computed with a composition solar and found that the ratio displayed a very similar dependence on mass. The presence in the H-band of spectral features sensitive to the masses of red giant stars opens up the potential of constraining more tightly the physical properties of the stars making up the galactic bulge and globular clusters.

UTILIZING SYNTHETIC VISIBLE SPECTRA TO EXPLORE THE PHYSICAL BASIS FOR THE CLASSIFICATION OF LAMBDA BOÖTIS STARS

ABSTRACT Since the peculiar nature of Lambda Boötis was first noticed in 1943, the Lambda Boo stars have been recognized as a group of peculiar A-type stars. They are Population I dwarfs that show deficiencies of iron-peak elements (up to 2 dex), but have near-solar C, N, O, and S abundances. In a previous paper, we used both observed and synthetic ultraviolet spectra to demonstrate that the C i 1657 Å/Al ii 1671 Å equivalent width ratio can help distinguish between Lambda Boo stars and other metal-weak stars hotter than 8000 K. In this paper, using observed and synthetic visible (4000–6800 Å) spectra, we demonstrate that the C i 5052.17 Å/Mg ii 4481 Å equivalent width ratio can be used as a quantitative diagnostic for cooler Lambda Boo stars.

Environmental impacts on dust temperature of star-forming galaxies in the local Universe

We present infrared views of the environmental effects on the dust properties in star-forming (SF) galaxies at z ~ 0, using the AKARI Far-Infrared Surveyor (FIS) all-sky map and the large spectroscopic galaxy sample from Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). We restrict the sample to those within the redshift range of 0.05 < z < 0.07 and the stellar mass range of 9.2 < log_10 (M_star/M_solar). We select SF galaxies based on their H_alpha equivalent width (EW_Ha> 4 A) and emission line flux ratios. We perform far-infrared (FIR) stacking analyses by splitting the SDSS SF galaxy sample according to their stellar mass, specific SFR (SSFR_SDSS), and environment. We derive total infrared luminosity (LIR) for each subsample using the average flux densities at WIDE-S (90 micron) and WIDE-L (140 micron) bands, and then compute IR-based SFR (SFR_IR) from L_IR. We find a mild decrease of IR- based SSFR (SSFR_IR) amongst SF galaxies with increasing local density (~0.1-dex level at maximum), which suggests that environmental effects do not instantly shut down the SF activity in galaxies. We also derive average dust temperature (T_dust) using the flux densities at 90 micron and 140 micron bands. We confirm a strong positive correlation between T_dust and SSFR_IR, consistent with recent studies. The most important finding of this study is that we find a marginal trend that T_dust increases with increasing environmental galaxy density. Although the environmental trend is much milder than the SSFR-T_dust correlation, our results suggest that the environmental density may affect the dust temperature in SF galaxies, and that the physical mechanism which is responsible for this phenomenon is not necessarily specific to cluster environments because the environmental dependence of T_dust holds down to relatively low-density environments.

A high fraction of double-peaked narrow emission lines in powerful active galactic nuclei

One percent of redshift z~0.1 Active Galactic Nuclei (AGNs) show velocity splitting of a few hundred km/s in the narrow emission lines in spatially integrated spectra. Such line profiles have been found to arise from the bulk motion of ionized gas clouds associated with galactic-scale outflows, merging pairs of galaxies each harboring a supermassive black hole (SMBH), and/or galactic-scale disk rotation. It remains unclear, however, how the frequency of narrow-line velocity splitting may depend on AGN luminosity. Here we study the correlation between the fraction of Type 2 AGNs with double-peaked narrow emission lines and AGN luminosity as indicated by [O III]5007 emission-line luminosity L_[O III]. We combine the sample of Liu et al. (2010) at z~0.1 with a new sample of 178 Type 2 AGNs with double-peaked [O III] emission lines at z~0.5. We select the new sample from a parent sample of 2089 Type 2 AGNs from the SDSS-III/Baryon Oscillation Spectroscopic Survey. We find a statistically significant (~4.2\sigma) correlation between L_[O III] and the fraction of objects that exhibit double-peaked narrow emission lines among all Type 2 AGNs, corrected for selection bias and incompleteness due to [O III] line width, equivalent width, splitting velocity, and/or equivalent width ratio between the two velocity components. Our result suggests that galactic-scale outflows and/or merging pairs of SMBHs are more prevalent in more powerful AGNs, although spatially resolved follow up observations are needed to resolve the origin(s) for the narrow-line velocity splitting for individual AGNs.

Shining a light on galactic outflows: photoionized outflows

We study the ionization structure of galactic outflows in 37 nearby, star forming galaxies with the Cosmic Origins Spectrograph on the Hubble Space Telescope. We use the O I, Si II, Si III, and Si IV ultraviolet absorption lines to characterize the different ionization states of outflowing gas. We measure the equivalent widths, line widths, and outflow velocities of the four transitions, and find shallow scaling relations between them and galactic stellar mass and star formation rate. Regardless of the ionization potential, lines of similar strength have similar velocities and line widths, indicating that the four transitions can be modeled as a co-moving phase. The Si equivalent width ratios (e.g. Si IV/Si II) have low dispersion, and little variation with stellar mass; while ratios with O I and Si vary by a factor of 2 for a given stellar mass. Photo-ionization models reproduce these equivalent width ratios, while shock models under predict the relative amount of high ionization gas. The photo-ionization models constrain the ionization parameter (U) between -2.25 < log(U) < -1.5, and require that the outflow metallicities are greater than 0.5 Z$_\odot$. We derive ionization fractions for the transitions, and show that the range of ionization parameters and stellar metallicities leads to a factor of 1.15-10 variation in the ionization fractions. Historically, mass outflow rates are calculated by converting a column density measurement from a single metal ion into a total Hydrogen column density using an ionization fraction, thus mass outflow rates are sensitive to the assumed ionization structure of the outflow.

On the cosmic evolution of Fe/Mg in QSO absorption line systems

We investigate the variation of the ratio of the equivalent widths of the Fe ii λ2600 line to the Mg ii λλ2796, 2803 doublet as a function of redshift in a large sample of absorption lines drawn from the Johns Hopkins University - Sloan Digital Sky Survey Absorption Line Catalog. We find that despite large scatter, the observed ratio shows a trend where the equivalent width ratio |$\mathcal {R}\equiv W_{\rm Fe\,\small {II}}/W_{\rm Mg\,\small {II}}$| decreases monotonically with increasing redshift z over the range 0.55 ≤ z ≤ 1.90. Selecting the subset of absorbers where the signal-to-noise ratio of the Mg ii equivalent width |$W_{\rm Mg\,\small {II}}\ {\rm is} \ge 3$| and modelling the equivalent width ratio distribution as a Gaussian, we find that the mean of the Gaussian distribution varies as |$\mathcal {R}\propto (-0.045\pm 0.005)z$|⁠. We discuss various possible reasons for the trend. A monotonic trend in the Fe/Mg abundance ratio is predicted by a simple model where the abundances of Mg and Fe in the absorbing clouds are assumed to be the result of supernova (SN) ejecta and where the cosmic evolution in the SNIa and core-collapse SN rates is related to the cosmic star formation rate. If the trend in |$\mathcal {R}$| reflects the evolution in the abundances, then it is consistent with the predictions of the simple model.

Elemental Abundance Analyses with DAO Spectrograms. XXXVIII. The SB2 Stars HR 104 (A2 V) and θ Aql (B9.5 III)

The study of the elemental abundances of double-lined spectroscopic binaries should provide information on the chemical differentiation of a once uniform prestellar nebula. To determine the effective temperatures and surface gravities of the primary and secondary stellar components of HR 104 and θ Aql, we used parameters derived from their orbital analyses and the requirement of equal abundances derived from Fe I and Fe II lines. For constraints we had optical region spectrophotometry for θ Aql and the large equivalent width ratios for the many spectral metal lines which were produced in both stellar atmospheres for HR 104. Since the primary stars were much brighter than the secondary stars, the abundances are considerably better determined for the primary stars. For HR 104 A we found T eff = 9875 K, log g = 4.26, and ξ = 1.7 km s-1; for HR 104 B T eff = 7200 K, log g = 4.26, and ξ = 0.6 km s-1; for θ Aql A T eff = 10400 K, log = 3.63, and ξ = 0.3 km s-1; and for θ Aql B T eff = 10250 K, log = 4.20, and ξ = 1.9 km s-1. The abundances of HR 104 A, HR 104 B, and θ Aql A are best described as the solar pattern. Those of θ Aql B suggest a weak nonmagnetic CP star pattern. While there is no trace of the Hg II 3984 line for θ Aql, the most extreme observed abundance anomalies for the secondary are those of Ca, V, Mn, and Ni. Further study of this hot marginal Am star could provide insights into the origin of the nonsolar chemical abundances.

Stellar parameters of early-M dwarfs from ratios of spectral features at optical wavelengths

(Abridged) Low-mass stars have been recognised as promising targets in the search for rocky, small planets with the potential of supporting life. Doppler search programmes using high-resolution spectrographs like HARPS or HARPS-N are providing huge quantities of optical spectra of M dwarfs. We aim to calibrate empirical relationships to determine stellar parameters for early M dwarfs (spectral types M0-M4.5) using the same spectra that are used for the radial velocity determinations. Our methodology consists in the use of ratios of pseudo equivalent widths of spectral features as a temperature diagnostic. Stars with effective temperatures obtained from interferometric estimates of their radii are used as calibrators. Empirical calibrations for the spectral type are also provided. Combinations of features and ratios of features are used to derive calibrations for the stellar metallicity. Our methods are then applied to a large sample of M dwarfs that are being observed in the framework of the HARPS search for extrasolar planets.The derived temperatures and metallicities are used together with photometric estimates of mass, radius, and surface gravity to calibrate empirical relationships for these parameters. A total of 112 temperature sensitive ratios have been calibrated over the range 3100-3950 K, providing Teff values with typical uncertainties of the order of 70 K. Eighty-two ratios of pseudo equivalent widths of features were calibrated to derive spectral types. Regarding stellar metallicity, 696 combinations of pseudo equivalent widths of individual features and temperature-sensitive ratios have been calibrated, over the metallicity range from -0.54 to +0.24 dex, with estimated uncertainties in the range of 0.07-0.10 dex. We provide our own empirical calibrations for stellar mass, radius, and surface gravity.

Disk dissipation timescale of pre-main sequence stars in Taurus

Abstract We present the results of an age determination study of pre-main sequence stars in the Taurus star-forming region. The ages of 10 single stars with masses of 0.5–1.1 M⊙ were derived from the surface gravities, estimated from high-resolution optical and near-infrared spectroscopy. The equivalent width ratios of nearby absorption line pairs were employed for the surface gravity diagnostic, which directly reflects the parameters of the stellar atmosphere without any veiling correction. From a comparison of determined ages and near-infrared color excesses such as J − H, J − K, and J − L, the inner disk lifetime of the young stars with 0.5–1.1 M⊙ in Taurus is estimated to be 3–4 Myr.

Early-type stars observed in the ESO UVES Paranal Observatory Project – IV. Studies of CN, CH+ and CH in the interstellar medium

High spectral resolution (∼80 000) and signal-to-noise observations from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project (UVES-POP) are used to study the interstellar molecular lines CN (3874 A), CH + (3957, 4232 A) and CH (3886, 4300 A) towards 74 O- and B-type stellar sightlines. Additionally, archive data are presented for 140 ELODIE early-type stellar sightlines at R = 42 000, plus 25 FEROS at R = 48 000 and 3 UVES at R > 50 000, mainly in the CH + (4232 A) and CH (3886, 4300 A) transitions. Detection rates are ∼45 per cent for CN and ∼67 per cent for the other lines in the POP sample, and ∼10–15 per cent for CH + and CH lines in the additional sample. CH and CH + are well correlated between log[N(CH) cm −2 ]∼12–14, implying that these clouds are CH + -like CH and not CN-like CH. CH is also very well correlated with Na I D in the range log[N(Na I cm −2 ]) ∼12.2–14.2. A few sightlines show tentative velocity shifts of ∼ 2k m s −1 between CH and CH + , which appear to be caused by differences in component strength in blends, and hence do not provide firm evidence for shocks. Finally, we describe a search for 13 CH + in a sightline towards HD 76341. No 13 CH + is detected, placing a limit on the 13 CH + to 12 CH + ratio of ∼0.01. If a formal fit is attempted, the equivalent width ratio in the two isotopes is a factor ∼90 but with large errors.

Hαobservations of theγ-ray-emitting Be/X-ray binary LSI+61°303: orbital modulation, disk truncation, and long-term variability

We report 138 spectral observations of the H-alpha emission line of the radio- and gamma-ray-emitting Be/X-ray binary LSI+61303 obtained during the period of September 1998 -- January 2013. From measuring various H-alpha parameters, we found that the orbital modulation of the H-alpha is best visible in the equivalent width ratio EW(B)/EW(R), the equivalent width of the blue hump, and in the radial velocity of the central dip. The periodogram analysis confirmed that the H-alpha emission is modulated with the orbital and superorbital periods. For the past 20 years the radius of the circumstellar disk is similar to the Roche lobe size at the periastron. It is probably truncated by a 6:1 resonance. The orbital maximum of the equivalent width of H-alpha emission peaks after the periastron and coincides on average with the X-ray and gamma-ray maxima. All the spectra are available upon request from the authors and through the CDS.

Characteristic times of wind variability in classical T Tauri stars

Results of observations of short-term wind variability in the classical T Tauri stars RW Aur and DR Tau are presented. Since the H CaII emission is absorbed by the absorption component of the H∈ line, which arises in the wind at a radial velocity of about −120 km/s, the ratio of equivalent widths of the H and K emission lines of ionized calcium is used as an indicator of the line-of-sight wind density. Observations showed that the wind densities of RW Aur and DR Tau vary with a characteristic time of 4 to 5 days, i.e., with a period that is somewhat shorter than the period of the axial rotation of these stars. These results are interpreted in the framework of the conical wind model, which predicts cyclic repetitions of accretion and ejection events caused by the interaction of the star’s magnetosphere with the ionized gas at the inner boundary of the accretion disc.

The GAPS programme with HARPS-N at TNG

A long-term multi-purpose observational programme has started with HARPS-N@TNG aimed to characterise the global architectural properties of exoplanetary systems. In this first paper we fully characterise the transiting system Qatar-1. We exploit HARPS-N high-precision radial velocity measurements obtained during a transit to measure the Rossiter-McLaughlin effect in the Qatar-1 system, and out-of-transit measurements to redetermine the spectroscopic orbit. New photometric transit light-curves are analysed and a spectroscopic characterisation of the host star atmospheric parameters is performed based on various methods (line equivalent width ratios, spectral synthesis, spectral energy distribution). We achieved a significant improvement in the accuracy of the orbital parameters and derived the spin-orbit alignment of the system; this information, combined with the spectroscopic determination of the host star properties, allows us to derive the fundamental physical parameters for star and planet (masses and radii). The orbital solution for the Qatar-1 system is consistent with a circular orbit and the system presents a sky-projected obliquity of lambda = -8.4+-7.1 deg. The planet, with a mass of 1.33+-0.05 M_J, is found to be significantly more massive than previously reported. The host star is confirmed to be metal-rich ([Fe/H]= 0.20+-0.10) and slowly rotating (vsinI = 1.7+-0.3 km/s), though moderately active, as indicated by strong chromospheric emission in the Ca II H&K line cores (logR'_HK about -4.60). The system is well aligned and fits well within the general lambda vs Teff trend. We definitely rule out any significant orbital eccentricity. The evolutionary status of the system is inferred based on gyrochronology, and the present orbital configuration and timescale for orbital decay are discussed in terms of star-planet tidal interactions.

Diffuse Interstellar Bands in M33

AbstractWe present the first sample of diffuse interstellar bands (DIBs) in the nearby galaxy M33. Studying DIBs in other galaxies allows the behaviour of the carriers to be examined under interstellar conditions which can be quite different from those of the Milky Way, and to determine which DIB properties can be used as reliable probes of extragalactic interstellar media. Multi-object spectroscopy of 43 stars in M33 has been performed using Keck/DEIMOS. The stellar spectral types were determined and combined with literature photometry to determine the M33 reddenings E(B-V)M33. Equivalent widths or upper limits have been measured for the λ5780 DIB towards each star. DIBs were detected towards 20 stars, demonstrating that their carriers are abundant in M33. The relationship with reddening is found to be at the upper end of the range observed in the Milky Way. The line of sight towards one star has an unusually strong ratio of DIB equivalent width to E(B-V)M33, and a total of seven DIBs were detected towards this star.

Small-scale structure in the interstellar medium: time-varying interstellar absorption towards κ Velorum

Ultra-high spectral resolution observations of time-varying interstellar absorption towards {\kappa} Vel are reported, using the Ultra-High Resolution Facility on the Anglo-Australian Telescope. Detections of interstellar Ca I, Ca II, K I, Na I and CH are obtained, whilst an upper limit on the column density is reported for C_2. The results show continued increases in column densities of K I and Ca I since observations ~ 4 yr earlier, as the transverse motion of the star carried it ~ 10 AU perpendicular to the line of sight. Line profile models are fitted to the spectra and two main narrow components (A & B) are identified for all species except CH. The column density N(K I) is found to have increased by 82 +10-9 % between 1994 and 2006, whilst N(Ca I) is found to have increased by 32 +- 5 % over the shorter period of 2002-2006. The line widths are used to constrain the kinetic temperature to T_k,A < 671 +18-17 K and T_k,B < 114 +15-14 K. Electron densities are determined from the Ca I / Ca II ratio, which in turn place lower limits on the total number density of n_A > 7 * 10^3 cm^-3 and n_B > 2 * 10^4 cm^-3. Calcium depletions are estimated from the Ca I / K I ratio. Comparison with the chemical models of Bell et al. (2005) confirms the high number density, with n = 5 * 10^4 cm^-3 for the best-fitting model. The first measurements of diffuse interstellar bands (DIBs) towards this star are made at two epochs, but only an upper limit of < 40 % is placed on their variation over ~ 9 years. The DIBs are unusually weak for the measured E(B-V) and appear to exhibit similar behaviour to that seen in Orion. The ratio of equivalent widths of the {\lambda}5780 to {\lambda}5797 DIBs is amongst the highest known, which may indicate that the carrier of {\lambda}5797 is more sensitive to UV radiation than to local density.