Observational Results of a Multi-Telescope Campaign in Search of Interstellar Urea [(NH2_2)2_2CO]

In this paper, we present the results of an observational search for gas phase urea [(NH$_2$)$_2$CO] observed towards the Sgr B2(N-LMH) region. We show data covering urea transitions from $\sim$100 GHz to 250 GHz from five different observational facilities: BIMA, CARMA, the NRAO 12 m telescope, the IRAM 30 m telescope, and SEST. The results show that the features ascribed to urea can be reproduced across the entire observed bandwidth and all facilities by best fit column density, temperature, and source size parameters which vary by less than a factor of 2 between observations merely by adjusting for telescope-specific parameters. Interferometric observations show that the emission arising from these transitions is cospatial and compact, consistent with the derived source sizes and emission from a single species. Despite this evidence, the spectral complexity, both of (NH$_2$)$_2$CO and of Sgr B2(N), makes the definitive identification of this molecule challenging. We present observational spectra, laboratory data, and models, and discuss our results in the context of a possible molecular detection of urea.Comment: 38 pages, 9 Figures, accepted in the Astrophysical Journa

TIMASSS: The IRAS16293-2422 Millimeter And Submillimeter Spectral Survey. I. Observations, calibration and analysis of the line kinematics

While unbiased surveys observable from ground-based telescopes have previously been obtained towards several high mass protostars, very little exists on low mass protostars. To fill up this gap, we carried out a complete spectral survey of the bands at 3, 2, 1 and 0.8 mm towards the solar type protostar IRAS16293-2422. The observations covered about 200\,GHz and were obtained with the IRAM-30m and JCMT-15m telescopes. Particular attention was devoted to the inter-calibration of the obtained spectra with previous observations. All the lines detected with more than 3 sigma and free from obvious blending effects were fitted with Gaussians to estimate their basic kinematic properties. More than 4000 lines were detected (with sigma \geq 3) and identified, yielding a line density of approximatively 20 lines per GHz, comparable to previous surveys in massive hot cores. The vast majority (~2/3) of the lines are weak and due to complex organic molecules. The analysis of the profiles of more than 1000 lines belonging 70 species firmly establishes the presence of two distinct velocity components, associated with the two objects, A and B, forming the IRAS16293-2422 binary system. In the source A, the line widths of several species increase with the upper level energy of the transition, a behavior compatible with gas infalling towards a ~1 Mo object. The source B, which does not show this effect, might have a much lower central mass of ~0.1 Mo. The difference in the rest velocities of both objects is consistent with the hypothesis that the source B rotates around the source A. This spectral survey, although obtained with single-dish telescope with a low spatial resolution, allows to separate the emission from 2 different components, thanks to the large number of lines detected. The data of the survey are public and can be retrieved on the web site http://www-laog.obs.ujf-grenoble.fr/heberges/timasss.Comment: 41 pages (26 pages of online Tables), 7 Tables and 6 Figure

О ВЛИЯНИИ ПОДСВЕТКИ НА ЭЛЕКТРОФИЗИЧЕСКИЕ ПАРАМЕТРЫ КОНТАКТОВ К ОБРАЗЦАМ CdTe

Voltage−current characteristics (VIC′s) were investigated and electric resistivity  and  Hall coefficient measurements  of high−ohmic cadmium telluride samples were made at room temperature. The samples were cut from ingots grown by traveling heater method and  doped with chlorine (2 • 1017 cm−3 in load). Indium and  gold were used as contact materials. Galvanomagnetic measurements  were made at  square−form samples using the  Van der  Pau  method in magnetic fields B ≤ 1.5 Tl. The near−contact regions were illuminated by white light of variable intensity; the  VIC′s were investigated also. In addition, the VIC′s were investigated when the sample was illu- minated by monochromatic 480 nm light through gold−covered sides of the sample. The experiments showed that  illumination  of the  near−contact region leads to a considerable decrease of sample resistance (by 2—3 orders of magnitude). The VIC′s had linear shapes and in most cases came through the  origin of coordinates. With an increase in the light intensity the angle between the X−axis and the VIC straight line increased. Similar results were obtained when monochromatic light passed through gold−covered sides of the sample. We show  that  illumination  of the  near−contact region allows measuring the electrical resistivity and the Hall coefficient of the sample which is impossible without illumination.Исследованы вольт−амперные характеристики (ВАХ) и проведены измерения удельного электрического сопротивления и коэффициента Холла образцов высокоомного теллурида кадмия при комнатной температуре. Исследованные образцы вырезаны из слитков, выращенных методом движущегося теплового поля и легированных хлором  на уровне ≈ 2 ⋅ 1017 см−3 (в шихте). В качестве контактных материалов использованы индий и золото. Измерения электрофизических параметров проведены на образцах квадратной формы по методу Ван− ер−Пау в диапазоне магнитных полей до 1,5  Тл в условиях регулируемой подсветки приконтактных областей белым светом. На этих же образцах исследованы ВАХ. Кроме того, ВАХ исследованы в условиях засветки образца монохроматическим излу- чением с длиной  волны 480 нм через покрытые  золотом грани образца. Установлено, что освещение областей вблизи контактов приводит к заметному (на два—три порядка) уменьшению сопротивления образца− двухполюсника. Обнаружено, что наблюдаемые ВАХ были линейными и в большинстве случаев проходили через начало  координат, что свидетельствует об отсутствии фото−ЭДС. При увеличении интенсивности подсветки  угол наклона ВАХ к оси абсцисс заметно увеличивался. Аналогичные результаты получены при засветке через золотое покрытие.  Показано, что подсветка приконтактных областей образца позволяет измерить удельное электрическое сопротивление и коэффициент Холла, что невозможно сделать в отсутствие подсветки

СПОСОБ РАЗДЕЛЬНОГО ОПРЕДЕЛЕНИЯ СОПРОТИВЛЕНИЙ ОБРАЗЦА ВЫСОКООМНОГО ПОЛУПРОВОДНИКА И КОНТАКТОВ К ОБРАЗЦУ

The method of separate determination of two−pole sample volume resistance and contact resistance is suggested. The method described is applicable to high−ohmic semiconductor samples: semiinsulating gallium arsenide, detector cadmium−zinc tel- luride (CZT), etc. The method is based on near−contact region illumination by monochromatic radiation of variable intensity from light emitting diodes with quantum energy exceeding band gap width of investigated material. It is necessary to obtain sample photo−current dependence upon light emitting diode current and to find the straight−line part of this dependence. The extrapola- tion of this linear part to ordinate axis gives cut−off current value. As bias voltage is known, it is easy to calculate sample volume resistance value. Afterwards, using dark current value, it is pos- sible to determine total contact resistance. The method was approbated on n−type semiinsulating GaAs sample. Contact resistance value was shown to be approximately equal to sample volume resistance. It means that influence of contacts must be taken into account when electrophysical data is analyzed.Предложен метод раздельного определения сопротивлений образца−двухполюсника и контактов к нему, который применим к образцам высокоомных полупроводниковых материалов: полуизолирующего арсенида галлия, детекторного теллурида кадмия−цинка (КЦТ) и др. Метод основан на засветке приконтакных областей образца моно- хроматическим излучением регулируемой интенсивности от светодиодов с энергией кванта, превышающей ширину запрещенной зоны исследуемого материала. Экстраполяция прямолинейного участка зависимости фототока через образец от тока через светодиоды к оси ординат позволяет найти ток отсечки, после чего по из- вестным значениям тока отсечки и напряжения смещения вычисляют значение сопротивления объема об- разца. Далее, зная темновое значение тока через образец, можно вычислить суммарное сопротивление контактов образца−двухполюсника. Метод опробован на образце полуизолирующего арсенида галлия n−типа электропроводности. Линейность контактов проверена по вольт−амперным характеристикам. Показано, что сопротивление контактов близко к сопротивлению объема образца, что подтверждает необходимость учета влияния контактов при анализе данных электрофизических измерений

WHAT IS THE NATURE OF THE DOUBLETS IN THE E-METHANOL LAMB-DIP SPECTRA?

Author Institution: Institute of Applied Physics of RAS, 46 Ul'yanova str., GSP-120, Nizhny Novgorod 603950; RussiaA large number of methanol lines have been measured with a Lamb-dip technique in the frequency range 75-510 GHz. A few series of doublets for the transitions with selection rules $\Delta J$ = 0, $\Delta K$ = $\pm$ 1, $\pm$ 3, $\pm$ 5, $E_1 \leftrightarrow E_2$ and $\Delta J$ = $\pm$ 1, $\Delta K$ = $\pm$ 1 between the torsional-rotational levels of E-methanol in the $\nu_t$ = 0 state have been observed. These doublets were not predicted and were not observed earlier. In a traditional approach to the methanol molecule (as a nearly prolate asymmetric top with an internal rotation) these doublets may only originate from the magnetic hyperfine structure of the $E$-methanol torsional-rotational levels. However, there are some signs in spectra indicating that the doublets are sensitive to the parity selections rules. If so, the origin of the doublets is an inversion splitting of the $E(+)$ and $E(-)$ energy levels. This exciting interpretation seems to be feasible. The results of the experimental measurements will be presented and the possibility of a new type of the inversion motion in the CH$_3$OH molecule due to the proton tunneling in the H-O-C-H plane will be discussed