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All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Classification of red variables

Red variables are traditionally classified into Mira, semiregular (SR), and slow irregular (L) variables. The Mira variables are the best defined subgroup, whereas SR and L stars are more numerous. The SR subgroup is additionally subdivided into: SRa variables, which feature regular variability with smaller pulsation amplitudes than Miras; SRb variables, which are less regular; SRc variables, which are more luminous; and SRd variables, which are warmer. Relationships within each group are not clear. An analysis of long-term American Association of Variable Star Observers (AAVSP) light curves is reported on. It is found that Mira-type variables are clearly different and distinguishable from SR variables. Similarly, M-type Miras and C-type Miras feature different light curve properties. The M-Miras form a homogeneous group. The pulsations of SR variables are unstable.

Mattei, Janet A.↗
DOE OSTI2024

Comparison of Sub-Ppm Instrument Response Suggests Higher Detection Limits Could Be Used to Quantify Methane Emissions from Oil and Gas Infrastructure

Quantifying and controlling fugitive methane emissions from oil and gas facilities remains essential for addressing climate goals, but the costs associated with monitoring millions of production sites remain prohibitively expensive. Current thinking, supported by measurement and simple dispersion modelling, assumes single-digit parts-per-million instrumentation is required. To investigate instrument response, the inlets of three trace-methane (sub-ppm) analyzers were collocated on a facility designed to release gas of known composition at known flow rates between 0.4 and 5.2 kg CH 4 h –1 from simulated oil and gas infrastructure. Methane mixing ratios were measured by each instrument at 1 Hertz resolution over nine hours. While mixing ratios reported by a cavity ring-down spectrometer (CRDS)-based instrument were on average 10.0 ppm (range 1.8 to 83 ppm), a mid-infrared laser absorption spectroscopy (MIRA)-based instrument reported short-lived mixing ratios far larger than expected (range 1.8 to 779 ppm) with a similar nine-hour average to the CRDS (10.1 ppm). We suggest the peaks detected by the MIRA are likely caused by a micrometeorological phenomenon, where vortex shedding has resulted in heterogeneous methane plumes which only the MIRA can observe. Further analysis suggests an instrument like the MIRA (an optical-cavity-based instrument with cavity size ≤10 cm3 measuring at ≥2 Hz with air flow rates in the order of ≤0.3 slpm at distances of ≤20 m from the source) but with a higher detection limit (25 ppm) could detect enough of the high-concentration events to generate representative 20 min-average methane mixing ratios. Even though development of a lower-cost, high-precision, high-accuracy instrument with a 25 ppm detection threshold remains a significant problem, this has implications for the use of instrumentation with higher detection thresholds, resulting in the reduction in cost to measure methane emissions and providing a mechanism for the widespread deployment of effective leak detection and repair programs for all oil and gas infrastructure.

03 NATURAL GAS↗
NASA NTRS2011

The Spectroscopic Evolution of the Symbiotic-like Recurrent Nova V407 Cygni During Its 2010 Outburst. 2. The Circumstellar Environment and the Aftermath

The nova outburst of V407 Cyg in 2010 Mar. 10 was the first observed for this star but its close resemblance to the well known symbiotic-like recurrent nova RS Oph suggests that it is also a member of this rare type of Galactic novae. The nova was the first detected at gamma-ray energies and is the first known nova explosion for this system. The extensive multiwavelength coverage of this outburst makes it an ideal comparison with the few other outbursts known for similar systems. We extend our previous analysis of the Mira and the expanding shock from the explosion to detail the time development of the photoionized Mira wind, circumstellar medium, and shocked circumstellar environment to derive their physical parameters and how they relate to large scale structure of the environment, extending the previous coverage to more than 500 days after outburst. We use optical spectra obtained at high resolution with the Nordic Optical Telescope (NOT) (R approx. =.45000 to 65000) and medium resolution Ondrejov Observatory (R approx. = 12000) data and compare the line variations with publicly available archival measurements at 30 GHz OVNR and at X-rays with Swift during the first four months of the outburst, through the end of the epoch of strong XR emission. We use nebular diagnostics and high resolution profile variations to derive the densities and locations of the extended emission. We find that the higher the ionization and/or the higher the excitation energy, the more closely the profiles resemble the He II/Ca V-type high velocity shock profile discussed in Paper I. This also accounts for the comparative development of the [N II] and [O III] isoelectronic transitions: the [O III] 4363A profile does not show the low velocity peaks while the excited [N II] 5754A does. If nitrogen is mainly N(+3) or higher in the shock, the upper state of the [N II] nebular lines will contribute but if the oxygen is O(+2) then this line is formed by recombination, masking the nebular contributor, and the lower states are collisionally quenched but emit from the low density surroundings. Absorption lines of Fe-peak ions formed in the Mira wind were visible as P Cyg profiles at low velocity before Day 69, around the time of the X-ray peak and we identified many absorption transitions without accompanying emission for metal lines. The H Balmer lines showed strong P Cyg absorption troughs that weakened during the 2010 observing period, through Day 128. The Fe-peak line profiles and flux variations were different for permitted and forbidden transitions: the E1 transitions were not visible after Day 128 but had shown a narrow peak superimposed on an extended (200 km/s) blue wing, while the M1 and E2 transitions persisted to Day 529, the last observation, and showed extended redshifted wings up of the same velocity. We distinguish the components from the shock, the photoionized environment, and the chromosphere and inner Mira wind using spectra taken more than one year after outburst. The multiple shells and radiative excitation phenomenology are similar to those recently cited for GRBs and SNIa .

Shore, S. N.↗
NASA NTRS2012

The Radio Light Curve of the Gamma-Ray Nova in V407 CYG: Thermal Emission from the Ionized Symbiotic Envelope, Devoured from Within by the Nova Blast

We present multi-frequency radio observations of the 2010 nova event in the symbiotic binary V407 Cygni, obtained with the Karl G. Jansky Very Large Array (VLA) and spanning 1.45 GHz and 17.770 days following discovery. This nova.the first ever detected in gamma rays.shows a radio light curve dominated by the wind of the Mira giant companion, rather than the nova ejecta themselves. The radio luminosity grewas the wind became increasingly ionized by the nova outburst, and faded as the wind was violently heated from within by the nova shock. This study marks the first time that this physical mechanism has been shown to dominate the radio light curve of an astrophysical transient. We do not observe a thermal signature from the nova ejecta or synchrotron emission from the shock, due to the fact that these components were hidden behind the absorbing screen of the Mira wind. We estimate a mass-loss rate for the Mira wind of .Mw approximately equals 10(exp -6) Solar mass yr(exp -1). We also present the only radio detection of V407 Cyg before the 2010 nova, gleaned from unpublished 1993 archival VLA data, which shows that the radio luminosity of the Mira wind varies by a factor of 20 even in quiescence. Although V407 Cyg likely hosts a massive accreting white dwarf, making it a candidate progenitor system for a Type Ia supernova, the dense and radially continuous circumbinary material surrounding V407 Cyg is inconsistent with observational constraints on the environments of most Type Ia supernovae.

Chomiuk, Laura↗
NASA NTRS1982

Observations and analysis of the R Aquarii jet

Ultraviolet, optical and radio observations of the symbiotic star R Aquarii are discussed in the light of the discovery of a bright radio and optical jet from this star. The star is probably a binary with a period of 44 years. The VLA maps of the jet reveal a protruding structure extending approximately 10 arc sec from the central radio source with a position angle virtually identical to that of the optical jet observed at Lick. The observations of R Aqr are interpreted as indicating the existence of an accretion disk around an unseen companion. The hot subdwarf has effective temperature approximately 65,000 K. It is suggested that the Mira primary and the hot secondary are in orbit around each other with a high eccentricity. At periastron the hot subdwarf accretes at super critical rates and a jet forms. It is difficult to understand how an accretion disk would have eclipsed the Mira in 1928-1935 and 1974-1980. The suppression of maximum light in these two periods is interpreted as due to a distortion of the Mira envelope at periastron by the tidal interaction with the secondary. The jet may help to explain the excitation of the R Aqr nebula. It is possible that R Aqr flared up as a nova approximately 1000 years ago forming the nebula.

Kafatos, M.↗
NASA NTRS1989

Dust formation around M-type stars

IRAS LRS spectra of M Mira variable have shown variation in the appearance of the 9.7 micron silicate feature, which is correlated with the shape of light curve. The LRS spectra of 100 Mira variables have been studied using simple dust shell models containing mixtures of silicate and aluminum oxide dust grains. It has been shown that the aluminum oxide grains account for the observed broad feature around 12 microns and that the variation of the spectra can be interpreted in terms of the variation of the temperature at the inner boundary of silicate dust shell. It has been proposed that silicate mantle growth on aluminum oxide grains is a possible explanation for the results. In this report, the model spectra are calculated taking account of silicate mantle growth, and the physical parameters which may determine the appearance of the 9.7 micron feature in M Mira variables are investigated. In the model calculation it is assumed that aluminum oxide grains are already formed at the bottom of the circumstellar envelope because of their high condensation temperature. The growth of silicate mantle and the motion of gas and grains from r=r(sub 0), where the mantle growth starts, are investigated. Sticking and sputtering processes due to the relative motion of grain to the ambient gas are taken into account. The thermal velocity is assumed to be negligible to the drift velocity. Acceleration by radiation pressure is considered in the gas motion equation. The formal solution is integrated to obtain the emergent spectra. Physical conditions inside r(sub 0) are regarded as boundary conditions. Observed spectra are compared to model spectra to investigate the conditions at the bottom of circumstellar envelope. In modeling the envelope, a parameter C(sub l) is introduced to take account of the density fluctuation of the envelope phenomenologically.

Onaka, Takashi↗
NASA NTRS1990

Preliminary interpretation of the Mg II variability of L2 Puppis

L2 Pup is perhaps the brightest SRb/Mira variable in the sky, with extreme variability from 2.6 to 6.2 magnitudes visually and a normal variation between 3.5 to 5.5. More than 60 percent of its cycles show large amplitude (2 magnitude) variation that is Mira like; however at intervals of 40 to 50 cycles it goes into a phase of smaller amplitude variability. One of the small amplitude episodes began in 1986 while L2 Pup was being observed with IUE (International Ultraviolet Explorer) as part of the monitoring program. During the first three observed cycles, Mg II emission in L2 Pup behaved in a manner similar to that in other normal Miras, and L2 Pup's light curve was also Mira like. However, during the fourth cycle there was an abrupt change in the Mg II emission, although the visual light curve remained normal through that cycle. In the next cycle the light curve also decreased in amplitude, and the Mg II emission remained anomalously low.

Brugel, Edward W.↗
NASA NTRS1992

Oxygen-rich semiregular and irregular variables

All the known oxygen-rich semiregulars and irregulars of spectral classes K and M with the absolute value of B not greater than 30 deg, Delta(m) not less than 0.5 mag, and, for the semiregulars, periods in the range of 50 to 400 d are compiled. On the basis of their distributions on the sky and their brightnesses in the K band at 2.2 microns, it is argued that the semiregulars with a period of 300-400 d appear to belong to the same population as the 'thin disk' Miras in the same period range and have an exponential scale height from the Galactic plane of about 250 pc. The semiregulars with a period range of 200 to 300 d belong to the population of the 'thick disk' Miras with an exponential scale height from the Galactic plane of about 500 pc. On the basis of the similarities of their space distributions and the presence of Tc in their atmospheres, and using the pulsational mode calculations by Ostlie and Cox (1986), it is suggested that the semiregulars with a period range of 100-150 d are first and second overtone pulsations of the same population of AGB stars as the Miras in their fundamental pulsational mode with periods longer than 300 d.

Jura, M.↗
NASA NTRS1999

Six Years of Short-Spaced Monitoring of the v=1 and v=2 J=1-0 (28)SiO Maser Emission in Evolved Stars

We present the results from a monitoring of the v=1 and v=2 J=1-0 (28)SiO maser emission in 21 objects, covering all types of known SiO maser emitters: 13 Mira variables, 2 long period semiregulars (SRGs), 3 variable supergiants (SGs), 2 OH/IR stars, and one young stellar object. This study has been carried out with the 13.7 meter radiotelescope of the Centro Astronomico de Yebes (Guadalajara, Spain), from July 1984 to May 1990, and represents the longest and most tightly sampled monitoring of SiO masers ever published. Our data show that for Mira-type (i.e. regular) variables, the SiO and optical light curves agree in period, and that the maxima of the SiO emission lag the optical ones by about 0.1-0.2 periods. Since a similar lag characterizes the near infrared (NIR) emission variability from these stars, we conclude that for regular variables SiO and NIR vary in phase. This result was confirmed in three objects for which NIR variability curves are available. For SRGs and SGs, we found a less systematic behavior, but when the SiO emission is periodic, its variability curve agrees with the optical one, also showing a lag between maximum epochs similar to that of Mira-type stars. The data clearly reveal other interesting details on the SiO maser variability, such as the strong intensity differences between different maxima and changes in the velocity distribution of the emission. Finally, the SiO masers associated to the young stellar object Orion IRc2 showed a double peaked spectrum with low amplitude, aperiodic variations.

Alcolea, J.↗
NASA NTRS2001

Observations of Circumstellar Material Around Evolved Stars With the ISI

The U.C. Berkeley Infrared Spatial Interferometer (ISI) is a stellar interferometer operating in the 9-12 micron region and has been in operation from 1988 until the present. It utilizes heterodyne detection using CO2 laser local oscillators and currently includes two 1.65 m movable telescopes mounted in semi-trailers and baselines up to about 65 m in length. A third telescope is being integrated with the other two and within the next year will operate as an imaging interferometer providing data with three simultaneous baselines and a closure phase, and baselines up to about 75 m. During the past twelve years the ISI has been used extensively for studies of circumstellar material around evolved stars. Multi-epoch observations of a sample of prototypical sources have elucidated the location and time scales for dust formation around these stars. These time scales can be as short as approx.10 years for Mira stars and as long as approx. 100 years for supergiants. For stars like Mira itself there is evidence for departure from spherical symmetry and episodes of dust formation and destruction. For some stars motion of dust has been observed -- IK Tau is one example, and NML Cyg is another. The molecules Silane and Ammonia were observed for the extreme carbon star IRC +10216 and the supergiant VY CMa pinpointing their location relative to the inner radius of the dust shell. Somewhat surprisingly, these molecules were found to form many stellar radii away from the inner radius of the dust shell, implying that they form by interactions with the surfaces of dust grains. Last year observations with the longest baselines lead to new precision diameters of $o$ Ceti and $\alpha$ Orionis, and are continuing on a somewhat larger set of Mira variable and supergiant stars.

Danchi, W. C.↗
NASA NTRS2011

The X-Ray Evolution of the Symbiotic Star V 407 Cygni During Its 2010 Outburst

We present a summary of Swift and Suzaku X-ray observations of the 2010 nova outburst of the symbiotic star, V 407 Cyg. The Suzaku spectrum obtained on day 30 indicates the presence of the supersoft component from the white dwarf surface, as well as optically thin component from the shock between the nova ejecta and the Mira wind. The Swift observations then allow us to track the evolution of both components from day 4 to day 150. Most notable is the sudden brightening of the optically think component around day 20. We identify this as the time when the blast wave reached the immediate vicinity of the photosphere of the Mira. We have developed a simplified model of the blast wave-wind interaction that can reproduce the gross features of the X-ray evolution of V407 Cyg. If the model is correct, the binary separation is likely to be large and the mass loss rate of the Mira is likely to be relatively low.

Mukai, K.↗
NASA NTRS2011

The X-Ray Evolution of the Symbiotic Star V407 Cygni During Its 2010 Outburst

We present a summary of Swift and Suzaku X-ray observations of the 2010 nova outburst of the symbiotic star, V407 Cyg. The Suzaku spectrum obtained on day 30 indicates the presence of the supersoft component from the white dwarf surface, as well as optically thin component from the shock between the nova ejecta and the Mira wind. The Swift observations then allow us to track the evolution of both components from day 4 to day 150. Most notable is the sudden brightening of the optically think component around day 20. We identify this as the time when the blast wave reached the immediate vicinity of the photosphere of the Mira. We have developed a simplified model of the blast wave-wind interaction that can reproduce the gross features of the X-ray evolution of V407 Cyg. If the model is correct, the binary separation is likely to be large and the mass loss rate of the Mira is likely to be relatively low.

Mukai, K.↗
NASA NTRS2020

Optical Spectroscopy and X-Ray Observations of the D-Type Symbiotic Star EF Aql

We performed high-resolution optical spectroscopy and X-ray observations of the recently identified Mira-type symbiotic star EF Aql. Based on high-resolution optical spectroscopy obtained with SALT, we determine the temperature (~55 000 K) and the luminosity (~5.3 L⨀) of the hot component in the system. The heliocentric radial velocities of the emission lines in the spectra reveal possible stratification of the chemical elements. We also estimate the mass-loss rate of the Mira donor star. Our Swift observation did not detect EF Aql in X-rays. The upper limit of the X-ray observations is 10(exp -12) erg cm(exp -2) s(exp -1), which means that EF Aql is consistent with the faintest X-ray systems detected so far. Otherwise, we detected it with the UVOT instrument with an average UVM2 magnitude of 14.05. During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter. The periodogram analysis of the V-band data reveals an improved period of 320.4±0.3 d caused by the pulsations of the Mira-type donor star. The spectra are available upon request from the authors.

Symbiotic binary stars↗