Sodium Lines Research Articles

Suppression of Rayleigh scattering noise in sodium laser guide stars by hyperfine depolarization of fluorescence

We propose what we believe is a novel method for enabling the complete suppression of noise due to Rayleigh scattering in sodium laser guide star systems by means of selective discrimination between Rayleigh and fluorescence signals based on polarization properties. We show that, contrary to the nearly 100% polarized Rayleigh scattering, fluorescence from the D(2) sodium line is strongly depolarized under excitation by a modeless laser. This offers the possibility of completely cancelling the effects of the Rayleigh scattering background while preserving the fluorescence signal to about 40% of its maximal value, leading to an improvement of the signal-to-noise ratio by several orders of magnitude. Both theoretical and experimental data confirm this new proposal.

GOLF-NG spectrometer, a space prototype for studying the dynamics of the deep solar interior

The GOLF-NG (Global Oscillations at Low Frequency New Generation) instrument is devoted to the search for solar gravity and acoustic modes, and also chromospheric modes from space. This instrument which is a successor to GOLF/SOHO will contribute to improve our knowledge of the dynamics of the solar radiative zone. It is a 15 points resonant scattering spectrometer, working on the D1 sodium line. A ground-based prototype is under construction to validate the difficult issues. It will be installed at the Teide Observatory, on Tenerife in 2006 to analyse the separation of the effects of the magnetic turbulence of the line from the solar oscillations. We are prepared to put a space version of this instrument including a capability of identification of the modes, in orbit during the next decade. This instrument should be included in the ILWS program as it offers a key to the improvement of our knowledge of the solar core in combination with observations from SDO and PICARD. We hope to determine the core rotation and magnetic field, through precise measurements of oscillation mode frequency splittings. Understanding the magnetic field of the radiative zone is important for progress in the study of solar activity sources, an important player for the long-term Sun–Earth relationship.

Seismic Emission from the Solar Flares of 2003 October 28 and 29

We report the detection of seismic waves emitted from powerful solar flares that occurred in NOAA Active Region 10486 on 2003 October 28 and 29. We used helioseismic holography to image the seismic sources of the waves. This technique was previously used to image the source of seismic emission from the large solar flare of 1996 July 9. Egression power maps at 6 mHz with a 2 mHz bandwidth reveal multiple compact acoustic sources strongly associated with the footpoints of a coronal loop that hosted the flares. The total acoustic energy in the flare signatures is a very small fraction of the total energy radiated by the flares. The acoustic signatures are co-aligned with hard X-ray signatures, suggesting a direct link between energetic particles accelerated during the flare and the acoustic waves as a hydrodynamic response of the chromosphere, or possibly the underlying photosphere, to these particles at the footpoints of the loop. There is also evidence of high-energy protons impinging onto the chromosphere in the neighborhoods of the acoustic sources. Observations of emission in the D1 line of neutral sodium at the onset of the October 29 flare show evidence of a downward-propagating shock/condensation at the onset of the flare. Concurrent Global Oscillation Network Group (GONG) intensity observations show significant radiative emission with a sudden onset in the compact region encompassing the acoustic signature. Most flares appear to be acoustically inactive. Photospheric heating by high-energy protons is likely to be a major factor in seismic emission from acoustically active flares.

Chiral Crystallization of Ethylenediamine Sulfate

Optimized conditions for the chiral crystallization of ethylenediamine sulfate, which can serve as an ideal undergraduate experiment, are described. Large, flat, colorless crystals of ethylenediamine sulfate are obtained in an undisturbed evaporation dish within a period of approximately five to seven days. The crystals are ideal for polarimetry studies and observation using Polaroid sheets. Students become familiar with polarizing filters and how they can be used to distinguish between dextrorotatory and levorotatory crystals. Of 100 randomly sampled crystals, 47 crystals showed a (+)-rotation, while 53 crystals showed a (-)-rotation. The absolute value of the average optical rotation of the 100 crystals was found to be 158/mm ± 2 for the D line of sodium. The relative direction of rotation of polarized light was also determined by simply observing the change in optical rotatory dispersion of the crystals placed between two Polaroid sheets as one of the sheets was rotated clockwise or counter clockwise.

Direct optical emission spectroscopy of liquid analytes using an electrolyte as a cathode discharge source (ELCAD) integrated on a micro-fluidic chip

Atomic emission detection of metallic species in aqueous solutions has been performed using a miniaturised plasma created within a planar, glass micro-fluidic chip. Detection was achieved using an Electrolyte as a Cathode Discharge source (ELCAD) in which the sample solution itself is used as the cathode for the discharge. To realise the ELCAD technique within a micro-fluidic device, a parallel liquid-gas flow was set up in a micro-channel and a glow discharge ignited between the flowing liquid sample surface and a metal wire anode. The detection of copper and sodium was achieved, using atmospheric pressure air as a carrier gas, by observation of atomic emission lines of copper at 324 nm, 327 nm, 511 nm, 515 nm and 522 nm and an atomic emission line of sodium at 589 nm using a commercially available miniaturised spectrometer. A total electrical power of less than 70 mW was required to sustain the discharge. A semi-quantitative, absolute detection limit of 17 nmol s(-1) was obtained for sodium with a sample flow rate of 100 microL min(-1) and an integration time of 100 ms in air at atmospheric pressure. The volume required for such detection is approximately 170 nL. Further analysis was performed with an Echelle spectrometer using both argon and air as a carrier gas. The geometry and flow rates used demonstrate the feasibility of integrating such micro-plasmas into other micro-fluidic devices, such as miniaturised CE devices, as a method of detection. The potential for using such micro-plasmas within highly portable miniaturised systems and mu-TAS devices is presented and discussed.

The Surface-Bounded Exosphere of Mercury

Almost thirty years ago, the instruments on the Mariner 10 spacecraft detected traces of hydrogen, helium, and possibly oxygen in the atmosphere of Mercury. There the matter rested until the mid-80’s, when emission lines of sodium (Potter & Morgan 1985) and potassium (Potter & Morgan 1986) were found in the spectrum of Mercury, resulting from resonance scattering of sunlight by metal atoms in the atmosphere. Searches for other metals in the Mercury atmosphere were fruitless until recently, when an emission line attributed to calcium has been observed (Bida, Killen & Morgan 2000). The densities of all these species are so low that gas phase collisions are negligible, so that the Mercury atmosphere is an exosphere bounded at its base by the surface of the planet. The fact that the exosphere is bounded by the Mercury surface means that interactions with the surface must occur. Energy exchange, surface absorption and desorption, and ion neutralization can take place, and these must be accounted for in models of the exosphere. None of these atmospheric species can survive long on Mercury, being lost mainly by photoionization followed by trapping in the solar wind and partly by solar radiation acceleration. Consequently, the species that we observe must be in a steady state, being generated as fast as they are lost to space. The metals must originate from the surface of the regolith, with the supply of fresh surface material maintained by gardening of the surface by meteoroid impact. The metals are released from the surface into the exosphere by photon-stimulated desorption (Madey et al. 1998), particle sputtering (McGrath, Johnson & Lanzerotti 1986), and meteoroid impact vaporization (Morgan, Zook & Potter 1988). Thermal evaporation of species condensed on the cold side may be important for determining their distribution over the planet (Hunten & Sprague 2002). The interaction and relative importance of all these processes has been discussed by Killen & Morgan (1993). Much can be said about these processes, but this review is focused primarily on the current status of observations of sodium, potassium, and calcium.

Diffuse Interstellar Bands in NGC 1448

We present spectroscopic VLT/UVES observations of two emerging supernovae, the Type Ia SN 2001el and the Type II SN 2003hn, in the spiral galaxy NGC 1448. Our high resolution and high signal-to-noise spectra display atomic lines of Ca  ,N a ,T i and K  in the host galaxy. In the line of sight towards SN 2001el, we also detect over a dozen diffuse interstel- lar bands (DIBs) within NGC 1448. These DIBs have strengths comparable to low reddening galactic lines of sight, albeit with some variations. In particular, a good match is found with the line of sight towards the σ type diffuse cloud (HD 144217). The DIBs towards SN 2003hn are significantly weaker, and this line of sight has also lower sodium column density. The DIB central velocities show that the DIBs towards SN 2001el are closely related to the strongest interstellar Ca  and Na  components, indicating that the DIBs are preferentially produced in the same cloud. The ratio of the λ 5797 and λ 5780 DIB strengths (r ∼ 0.14) suggests a rather strong UV field in the DIB environment towards SN 2001el. We also note that the extinction estimates obtained from the sodium lines using multiple line fitting agree with reddening estimates based on the colors of the Type Ia SN 2001el.

Detection of neutral sodium above Mercury during the transit on 2003 May 7

The extent of the exosphere of Mercury above the planet's limb could for the first time be observed by detecting an excess absorption in the solar sodium line D 2 during the transit of Mercury across the solar disk on 2003 May 7. The observations were performed with a 2d Fabry-Perot spectrograph of the Vacuum Tower Telescope at Izana, Tenerife. The absorption excess, blue-shifted by 13 pm relative to the solar line, is mainly concentrated near the polar regions. There, the absorption excess can be traced up to ≈ 700 km above the limb. Between the two polar regions, along the eastern limb, a weaker absorption excess can be seen. A possible streamer-like feature stretches more than 2000 km above the northern region. Assuming the density to decrease exponentially with height, we derive for the polar maxima vertical column densities of 3 $\times$ $10^{10}~{\rm cm}^{-2}$, volume densities at the surface of 2.5 $\times$ $10^3~{\rm cm}^{-3}$, and a density scale height of 150 km.

Center-to-limb variation of solar line profiles as a test of NLTE line formation calculations

We present new observations of the center-to-limb variation of spectral lines in the quiet Sun. Our long-slit spectra are corrected for scattered light, which amounts to 4-8 % of the continuum intensity, by comparison with a Fourier transform spectrum of the disk center. We examine the effect of inelastic collisions with neutral hydrogen in NLTE line formation calculations of the oxygen infrared triplet, and the Na I 6160.8 A line. Adopting a classical one-dimensional theoretical model atmosphere, we find that the sodium transition, formed in higher layers, is much more effectively thermalized by hydrogen collisions than the high-excitation oxygen lines. This result appears as a simple consequence of the decrease of the ratio NH/Ne with depth in the solar photosphere. The center-to-limb variation of the selected lines is studied both under LTE and NLTE conditions. In the NLTE analysis, inelastic collisions with hydrogen atoms are considered with a simple approximation or neglected, in an attempt to test the validity of such approximation. For the sodium line studied, the best agreement between theory and observation happens when NLTE is considered and inelastic collisions with hydrogen are neglected in the rate equations. The analysis of the oxygen triplet benefits from a very detailed calculation using an LTE three-dimensional model atmosphere and NLTE line formation. The chi**2 statistics favors including hydrogen collisions with the approximation adopted, but the oxygen abundance derived in that case is significantly higher than the value derived from OH infrared transitions.

Light pollution at the Roque de los Muchachos Observatory

Sky spectra were obtained from archival science frames taken with DoLoRes at the 3.58 m Telescopio Nazionale Galileo with a wavelength range ∼3800–8000 Å and resolution of 2.8 and 3.6 Å/pix. Our spectra include all the important sodium and mercury light pollution lines and span a wide interval of azimuth and observing conditions, essential to disentangle environmental and seasonal effects. New sodium and mercury lines were also detected for the first time at the observatory. Light pollution from NaD5892–8 emitted by the LPS lamps increased by a factor of 1.5–2 with respect to the average values of 1998. At the same time, light pollution from Hg lines decreased by ∼40% and reaches the 1998 levels only when observing toward the towns. The contribution of NaD5892–8 from LPS lamps to sky background is 0.05–0.10 mag at V-band and 0.07–0.12 mag at R-band. Synthetic sky brightness measures calculated from our spectra at V, B and R bands are in good agreement with those of [Benn, C.R., Ellison, S.L., 1998. La Palma Technical Note, p. 115] if we take into account that our observations were done during 2003, 7 years after the last sunspot minimum. The effects of the application of the Canary Sky Law are directly visible in the spectra as a 50% dimming of the Hg light-polluting lines in the spectra taken after local midnight.

Non-LTE Analysis of the Sodium Abundance of Metal-Poor Stars in the Galactic Disk and Halo

We performed an extensive non-LTE analysis of the neutral sodium lines of Na {\sc i} 5683/5688, 5890/5896, 6154/6161, and 8183/8195 for disk/halo stars of F--K type covering a wide metallicity range ($-4 \la$ [Fe/H] $\la 0.4$), based on our own data as well as those collected from the literature. For comparatively metal-rich disk stars ($-1 \la$ [Fe/H] $\la 0$) where the weaker 6154/6161 lines are best abundance indicators, we confirmed [Na/Fe] $\sim$ 0 with an ``upturn'' (i.e., a shallow/broad dip around $-0.5 \la$ [Fe/H] $\la 0$) as already reported by previous studies. Regarding the metal-deficient halo stars, where the much stronger 5890/5896 or 8183/8195 lines suffering considerable (negative) non-LTE corrections amounting to 0.5 dex have to be used, our analysis suggests mildly ``subsolar'' [Na/Fe] values down to $\sim -0.4$ (with a somewhat large scatter of $\sim \pm 0.2$ dex) on the average at the typical halo metallicity of [Fe/H] $\sim -2$, while they appear to rise again toward a very metal-poor regime recovering a near-solar ratio of [Na/Fe] $\sim$ 0 ([Fe/H] $\sim -3$ to -4). These results are discussed in comparison with the previous observational studies along with the theoretical predictions from the available chemical evolution models.

On the Indirect Detection of Sodium in the Atmosphere of the Planetary Companion to HD 209458

Using a self-consistent atmosphere code, we construct a new model of the atmosphere of the transiting extrasolar giant planet HD 209458b to investigate the disparity between the observed strength of the sodium absorption feature at 589 nm and the predictions of previous models. For the atmospheric temperature-pressure profile we derive, silicate and iron clouds reside at a pressure of several millibars in the planet's atmosphere. These clouds have significant vertical extent and optical depth because of our slant viewing geometry and lead to increased absorption in bands directly adjacent to the sodium line core. Using a non-LTE sodium ionization model that includes photoionization by stellar UV flux, collisional processes with H2, and radiative recombination, we show that the ionization depth in the planet's atmosphere reaches ~ mbar at the day/night terminator. Ionization leads to a slight weakening of the sodium feature. We present our baseline model, including ionization and clouds, which falls near the observational error bars. The sensitivity of our conclusions to the derived atmospheric temperature-pressure profile is discussed.

Dynamical Processes in the Neighborhood of the Herbig Ae Star MWC 480 Based on Spectral Monitoring Data

Spectral observations of the Herbig Ae star MWC 480 are reported. Observations were made on the 2.6 m telescope at the Crimean Astrophysical Observatory and the 6 m telescope at the Special Astrophysical Observatory in the neighborhoods of the sodium resonance doublet, the He I λ5876 A line, the oxygen O I λ7774 A line, the Hα line, and some others. The Hα line has a P Cyg-type profile which is typical of anisotropic decelerated material outflows. The parameters of the line profile vary on a time scale on the order of days or longer. The blue wing of the line profile, in which noticeable changes are detectable over times of a few hours, is subject to the greatest variation. An unusual line shape is observed in the sodium lines. Their profiles resemble type P Cyg profiles with discrete absorption components can be seen in the blue wing. The number, shape, and radial velocities of the components change with time. The maximum radial velocity is -330 km/s and the minimum, about -50 km/s. The high velocity components are subject to the greatest variability. An analysis of the spectral variability yields the following conclusions: (1) the inner layers of the accretion disk of MWC 480 reach right to the star. The maximum rotation velocity of the circumstellar gas derived from the oxygen OI 7774 A line shape is close to 400-500 km/s, which corresponds roughly to the radius of the last Keplerian orbit. (2) A highly nonuniform, high velocity component of the disk wind, which contains dense fragments (microjets), develops in this region. They appear to form as a result of the unstable structure of the magnetic field in the layers of the accretion disk closest to the star. (3) The maximum velocities of the microjets are only slightly higher than the escape velocity at the star's surface. Thus, the bulk of the momentum which they acquire is expended in overcoming the star's gravity and this causes a deceleration in the radial motion of the gas. This kind of structure for the radiating region is consistent with magneto-centrifugal models of the disk wind in which the intrinsic magnetic field of the accretion disk plays a dominant role in the acceleration of the gas.

Evolution of the Fu Orionis Object BBW 76

We have carried out a long-term photometric and spectroscopic monitoring program of the southern FU Orionis–type object BBW 76 spanning the period from 1982 to 1997. BBW 76 has the same radial velocity as the small cloud toward which it is projected, and for which a kinematic distance of about 1.8 kpc has been derived. We have determined a large reddening of E(B-V) ~ 0.7 for BBW 76. Optical and infrared spectra show the change toward later spectral type with increasing wavelength characteristic of FU Orionis stars and indicative of a hot luminous disk. High-resolution echelle spectra of BBW 76 show P Cygni profiles with extended blueshifted absorption troughs at the Hα and sodium lines from a neutral, supersonic wind. Comparison of such spectra obtained at six different epochs between 1985 and 1997 reveals major changes in these Hα and sodium line profiles. For a period of 10 years from 1985, the massive absorption troughs diminished in extent and depth, until by 1994 they had all but disappeared, while at the same time the blueshifted emission peak in the Hα line increased markedly in strength. However, when observed in 1997, the absorption had increased again and the emission had diminished. We interpret this in terms of an extended period during which accretion through a circumstellar disk decreased, with a resulting decrease in wind production. But the increased activity by 1997 shows that this is not a constant decay and that the star was not about to revert to its presumably original T Tauri stage. We monitored the star with optical photometry from 1983 to 1994, during which period it decreased almost monotonically in brightness by 0.2 mag in V. Infrared J, H, and K photometry from 1983 to 1991 shows a period of monotonic fading between 1984 and 1988, followed by more irregular behavior. In a search of the Harvard plate archives we have found a plate from the year 1900 on which BBW 76 is seen at approximately its present brightness, certainly not 2 mag brighter as expected if the optical decline between 1983 and 1994 had persisted during the whole century. Also, a plate taken for the Franklin-Adams charts in 1927 again shows BBW 76 at approximately the same brightness. This historical light curve makes BBW 76 the FU Orionis star with the longest-documented period in a high state. Overall, the observations suggest that BBW 76 is virtually identical to the prototype of its class, FU Orionis itself, in all respects except that BBW 76 has not shown the regular fading that FU Orionis has displayed after its eruption in 1936. This may be due to continued replenishment of the circumstellar accretion disk.

Theoretical Spectral Models of T Dwarfs at Short Wavelengths and Their Comparison with Data

We have generated new, self-consistent spectral and atmosphere models for the effective temperature range 600-1300 K thought to encompass the known T dwarfs. For the first time, theoretical models are compared with a family of measured T dwarf spectra at wavelengths shortward of ~1.0 μm. By defining spectral indices and standard colors in the optical and very near-infrared, we explore the theoretical systematics with Teff, gravity, and metallicity. We conclude that the short-wavelength range is rich in diagnostics that complement those in the near-infrared now used for spectral subtyping. We also conclude that the wings of the Na D and K I (7700 A) resonance lines and aggressive rainout of heavy metals (with the resulting enhancement of the sodium and potassium abundances at altitude) are required to fit the new data shortward of 1.0 μm. Furthermore, we find that the water bands weaken with increasing gravity, that modest decreases in metallicity enhance the effect in the optical of the sodium and potassium lines, and that at low values of Teff, in a reversal of the normal pattern, optical spectra become bluer with further decreases in Teff. Moreover, we conclude that T dwarf subtype is not a function of Teff alone but that it is a nontrivial function of gravity and metallicity as well. As do Marley and coworkers in their 2002 work, we see evidence in early T dwarf atmospheres of a residual effect of clouds. With cloudless models, we obtain spectral fits to the two late T dwarfs with known parallaxes, but a residual effect of clouds on the emergent spectra of even late T dwarfs cannot yet be discounted. However, our focus is not on detailed fits to individual objects but on the interpretation of the overall spectral and color trends of the entire class of T dwarfs, as seen at shorter wavelengths.

On the Red Rectangle optical emission bands

We have observed the Red Rectangle nebula with the Multi-Object Spectrograph on the WIYN telescope. Moderate-resolution spectra (Δλ=0.4 A) in the region of 5800 A were obtained in 3-arcsec apertures at over 50 positions in the nebula. Accurate and precise wavelength calibrations were obtained against a thorium–argon lamp and the sodium lines in the sky and nebula. The peak position and full width at half-maximum of the 5800-A Red Rectangle band (RRB) were measured to beyond 15 arcsec from the star. The shortest wavelength of the band is found to be 5799.10±0.15 A in the rest frame of the nebula. None of the emission bands has intensity coincident with the wavelength of the diffuse interstellar band (DIB) at 5797.11±0.05 A. The 2-A offset cannot be explained by an instrumental, spectroscopic or photophysical effect. The hypothesis that the same molecule may be the carrier of the RRB and the DIB is contradicted by these observations. As a further test of the hypothesis, absorption has been sought that would be due to a potential DIB carrier in the nebula. Tentative evidence for absorption is found in the RRB spectra taken within 9 arcsec of the star; but any absorption has a peak position essentially coincident in wavelength with the band maximum of the emission band.

Comments on alternative calculations of the broadeningof spectral lines of neutral sodium by H-atom collisions

With the exception of the sodium D-lines, recent calculations ofline broadening cross sections for several multiplets of sodiumby Leininger et al (Leininger T, Gadéa F X and Dickinson A2000 J. Phys. B: At. Mol. Opt. Phys. 33 1805) are in substantial disagreement withcross sections interpolated from the tables of Anstee andO'Mara (Anstee and O'Mara 1995 Mon. Not. R. Astron. Soc.276 859) and Barklem and O'Mara (Barklem P S and O'Mara B J 1997Mon. Not. R. Astron. Soc. 290 102). The discrepancyis as large as a factor of 3 for the 3p-4d multiplet. Thetwo theories are tested by using the results of each tosynthesize lines in the solar spectrum. It is found thatgenerally the data from the theory of Anstee, Barklem and O'Maraproduce the best match to the observed solar spectrum. It isfound, using a simple model for reflection of the opticalelectron by the potential barrier between the two atoms, thatthe reflection coefficient is too large for avoided crossingswith the upper states of subordinate lines to contribute to linebroadening, supporting the neglect of avoided ionic crossingsby Anstee, Barklem and O'Mara for these lines. The largediscrepancies between the two sets of calculations is a resultof an approximate treatment of avoided ionic crossings for theselines by Leininger et al (Leininger T, Gadéa F X andDickinson A 2000 J. Phys. B: At. Mol. Opt. Phys. 33 1805).

The resonance escape factor for Voigt and Lorentz line profiles in atomic absorption measurements

The resonance escape factor Λ r of two resonance lines of sodium at 3303 and 5890 A ̊ and strontium at 4078 and 4607 A ̊ have been determined from atomic absorption measurements of the radiation emitted from sodium and strontium hollow cathode lamps. The calculations have been carried out for dispersion (Lorentz) and Voigt broadened line profiles for the flame at a temperature of 2400 K. The dependence of the escape factors on the optical depth τ o in the line center is considered. The change of resonance escape factors with the total number of absorbing atoms in the ground state N ( cm −3) averaged over a length L is also discussed.

TEMPERATURE MEASUREMENT OF SOLID ROCKET MOTOR EXHAUST PLUME BY ABSORPTION-EMISSION SPECTROSCOPY1*

A method, which measures the temperature of solid rocket motor exhaust plume, was developed by employing an improved sodium line reversal process. The formula for calculating the temperature was improved and simplified. The temporal temperature-time distributions of the exhaust plume of double base propellant rocket motors were given by the established method. The maximum time resolution and accuracy for the temperature measurement are 40 μs and 8%, respectively. This kind of temperature measurement does not disturb the combustion flow field of exhaust plume and is simpler and more sensitive. The maximum temperatures of SQ-2 propellant exhaust plumes are 2234 K and 2202 K for 240 mm and 500 mm apart from the motor nozzle, respectively. More combustion phenomena of the exhaust plume can be measured by using an existing instrument.

Behavior of the Line Profiles of the Sodium Doublet and the Calcium Triplet in the Spectrum of R CrB in the Shallow Minima of 1998-1999

The behavior of profiles of the Na I D line and of the infrared Ca II triplet for the star R Coronae Borealis (R CrB) during shallow light minima of 1998-1999 is traced using high-resolution spectra. During a light maximum, the sodium lines had an absorption profile with a shift of —(2-4) km/sec. During a light minimum, a narrow emission feature, which has an almost constant absolute intensity and a shift of —(8-10) km/sec, and an intense circumstellar absorption feature, which has a variable profile and a variable relative shift corresponding to an increase to 220 km/sec in the velocity of mass ejection, appeared in the cores of absorption lines. For several days before the onset of a light minimum, all three calcium lines exhibited a narrow emission feature in the line core with a shift of —(1-5) km/sec. All the subsequent changes in a line involved mainly the shape of the absorption line profile. The narrow emission feature's absolute intensity and relative position were maintained during all our observations. The behavior of the Na I D line profiles can be described qualitatively within the framework of the model of a spherical dust shell.