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Publications (24)36.63 Total impact

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    ABSTRACT: Cyanogen (NCCN) is the simplest member of the series of dicyanopolyynes. It has been hypothesized that this family of molecules can be important constituents of interstellar and circumstellar media, although the lack of a permanent electric dipole moment prevents its detection through radioastronomical techniques. Here we present the first solid evidence of the presence of cyanogen in interstellar clouds through the detection of its protonated form toward the cold dark clouds TMC-1 and L483. Protonated cyanogen (NCCNH+) has been identified through the J=5-4 and J=10-9 rotational transitions using the 40m radiotelescope of Yebes and the IRAM 30m telescope. We derive beam averaged column densities for NCCNH+ of (8.6+/-4.4)e10 cm-2 in TMC-1 and (3.9+/-1.8)e10 cm-2 in L483, which translate to fairly low fractional abundances relative to H2, in the range (1-10)e-12. The chemistry of protonated molecules in dark clouds is discussed, and it is found that, in general terms, the abundance ratio between the protonated and non protonated forms of a molecule increases with increasing proton affinity. Our chemical model predicts an abundance ratio NCCNH+/NCCN of 1e-4, which implies that the abundance of cyanogen in dark clouds could be as high as (1-10)e-8 relative to H2, i.e., comparable to that of other abundant nitriles such as HCN, HNC, and HC3N.
    Astronomy and Astrophysics 06/2015; 579. DOI:10.1051/0004-6361/201526650 · 4.48 Impact Factor
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    ABSTRACT: This letter presents the design and performance of a noise source module for in-situ noise temperature measurements at cryogenic temperatures. The noise source module operates from DC up to 50 GHz and is suitable for measurements of noise temperatures as low as a few Kelvin, achieving a measurement accuracy of about $pm {1.2}~{rm K}$. The GaAs MMIC used in the module includes a well matched 50 $Omega$ termination with better than 20 dB return loss, a heating element and an on-chip temperature sensor, hence the noise source module can directly be connected to the device under test (DUT) with no additional elements or transitions needed. The measurement can then be taken with standard noise measurement equipment. Noise temperatures as low as 13 K have been measured in Ka-band with this device. Due to the ease of use, the good matching, the extraordinary bandwidth and the less involved calibration technique, the noise source module outperforms the conventional measurement setup using a noise diode in conjunction with a cooled attenuator.
    IEEE Microwave and Wireless Components Letters 12/2012; 22(12):657-659. DOI:10.1109/LMWC.2012.2228176 · 2.24 Impact Factor
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    ABSTRACT: MMIC Broadband Low Noise Amplifiers (LNA) for radio astronomy applications with 100 nm GaAs metamorphic High Electron Mobility Transistor (mHEMT) process have been developed. Cryogenic performance of a 4–12 GHz and a 25–34 GHz LNAs is presented. The 4–12 GHz LNA cooled at 15 K exhibits an associated gain of 31.5 dB ± 1.8 dB and average noise temperature of 5.3 K with a low power dissipation of 8 mW. Cooled to 15 K the 25–34 GHz amplifier has demonstrated a flat gain of 24.2 dB ± 0.4 dB with 15.2 K average noise temperature, and a very low power dissipation of 2.8 mW on chip. The mHEMT based LNA MMICs have demonstrated excellent noise characteristics at cryogenic temperatures for their use in radio astronomy applications.
    2012 IEEE MMT-S International Microwave Symposium Digest (MTT); 06/2012
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    ABSTRACT: Two broadband very low-noise amplifiers operating in the frequency range from 4 to 12 GHz at cryogenic temperature are presented. The amplifier circuits have been developed using a 100 nm gate length InAlAs/InGaAs metamorphic high electron mobility transistor (mHEMT) technology. The three-stage amplifiers are monolithic microwave integrated circuit (MMIC) chips manufactured in coplanar technology. At cryogenic temperature the first MMIC amplifier achieved a linear gain of 22 dB and an average noise temperature of 11.6 K with a power dissipation of 41 mW. The second MMIC amplifier, with external input matching network, exhibited a gain of 26 dB, and an excellent average noise temperature of 8.1 K with a power dissipation of 12 mW. Both LNA units demonstrate broad bandwidth, high gain, low noise temperature, and compact chip size. The results obtained prove that mHEMT technology is suitable for applications in large instantaneous bandwidth cryogenic receivers for radio astronomy applications.
    IEEE Microwave and Wireless Components Letters 12/2011; DOI:10.1109/LMWC.2011.2167502 · 2.24 Impact Factor
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    ABSTRACT: InP HEMTs provide the best available low-noise transistor performance. The availability of InP HEMTs for cryogenic front-ends is of paramount importance in ultra-low noise Deep-Space Network (DSN) and Radio-Astronomy (RA) applications. In DSN applications, cryo-cooled InP HEMT front-ends are at the heart of the ESA 34 m antennas used to detect data carrying signals and telemetry information from deep space probes, and excellent HEMT noise performances are key to reducing antenna size and cost, as well as to simplifying spacecraft payloads. In RA, very low noise temperatures are required because of the cold cosmic microwave background (~2.73K).
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    ABSTRACT: During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the highresolution HIFI spectrometer onboard Herschel. We report on the first detection of H16 2 O and the rarer isotopologues H17 2 O and H18 2 O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6 × 10−5, and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H2O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12CO, 13CO, 28SiO, 29SiO, 30SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.
    Astronomy and Astrophysics 10/2010; 521. DOI:10.1051/0004-6361/201015069 · 4.48 Impact Factor
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    ABSTRACT: We performed Herschel/HIFI observations of several CO lines in the far-infrared/sub-mm in the protoplanetary nebula CRL618. The high spectral resolution provided by HIFI allows measurement of the line profiles. Since the dynamics and structure of the nebula is well known from mm-wave interferometric maps, it is possible to identify the contributions of the different nebular components (fast bipolar outflows, double shells, compact slow shell) to the line profiles. The observation of these relatively high-energy transitions allows an accurate study of the excitation conditions in these components, particularly in the warm ones, which cannot be properly studied from the low-energy lines. The 12CO J=16-15, 10-9, and 6-5 lines are easily detected in this source. 13CO J=10-9 and 6-5 are also detected. Wide profiles showing spectacular line wings have been found, particularly in 12CO 16-15. Other lines observed simultaneously with CO are also shown. Our analysis of the CO high-J transitions, when compared with the existing models, confirms the very low expansion velocity of the central, dense component, which probably indicates that the shells ejected during the last AGB phases were driven by radiation pressure under a regime of maximum transfer of momentum. No contribution of the diffuse halo found from mm-wave data is identified in our spectra, because of its low temperature. We find that the fast bipolar outflow is quite hot, much hotter than previously estimated; for instance, gas flowing at 100 km/s must have a temperature higher than ~ 200 K. Probably, this very fast outflow, with a kinematic age < 100 yr, has been accelerated by a shock and has not yet cooled down. The double empty shell found from mm-wave mapping must also be relatively hot, in agreement with the previous estimate.
    Astronomy and Astrophysics 10/2010; 521. DOI:10.1051/0004-6361/201015068 · 4.48 Impact Factor
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    ABSTRACT: Aims. This paper describes the Heterodyne Instrument for the Far-Infrared ( HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods. The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 x 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 kms(-1). Result. After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations.
    Astronomy and Astrophysics 07/2010; 518. DOI:10.1051/0004-6361/201014698 · 4.48 Impact Factor
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    ABSTRACT: The molecular gas in the DR21 massive star formation region is known to be affected by the strong UV field from the central star cluster and by a fast outflow creating a bright shock. The relative contribution of both heating mechanisms is the matter of a long debate. By better sampling the excitation ladder of various tracers we provide a quantitative distinction between the different heating mechanisms. HIFI observations of mid-J transitions of CO and HCO+ isotopes allow us to bridge the gap in excitation energies between observations from the ground, characterizing the cooler gas, and existing ISO LWS spectra, constraining the properties of the hot gas. Comparing the detailed line profiles allows to identify the physical structure of the different components. In spite of the known shock-excitation of H2 and the clearly visible strong outflow, we find that the emission of all lines up to > 2 THz can be explained by purely radiative heating of the material. However, the new Herschel/HIFI observations reveal two types of excitation conditions. We find hot and dense clumps close to the central cluster, probably dynamically affected by the outflow, and a more widespread distribution of cooler, but nevertheless dense, molecular clumps. Comment: Accepted for publication by A&A
    Astronomy and Astrophysics 05/2010; 518. DOI:10.1051/0004-6361/201014579 · 4.48 Impact Factor
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    ABSTRACT: Millimetron is a Russian-led 12m diameter submillimeter and far-infrared space observatory which is included in the Space Plan of the Russian Federation for launch around 2017. With its large collecting area and state-of-the-art receivers, it will enable unique science and allow at least one order of magnitude improvement with respect to the Herschel Space Observatory. Millimetron will be operated in two basic observing modes: as a single-dish observatory, and as an element of a ground-space very long baseline interferometry (VLBI) system. As single-dish, angular resolutions on the order of 3 to 12arc sec will be achieved and spectral resolutions of up to a million employing heterodyne techniques. As VLBI antenna, the chosen elliptical orbit will provide extremely large VLBI baselines (beyond 300,000km) resulting in micro-arc second angular resolution.
    Experimental Astronomy 03/2009; 23(1):221-244. DOI:10.1007/s10686-008-9097-6 · 2.66 Impact Factor
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    Juan Daniel Gallego · Isaac López-Fernández · Carmen Diez · Alberto Barcia
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    ABSTRACT: Applications like radio astronomy and space communications require ultimate sensitivity and make use of very particular receivers with state-of-the-art devices. Usually the receivers are cooled at cryogenic temperatures to reduce the noise even further. Noise temperatures of only a few times the quantum limit can be obtained in these conditions. During the past decade, Indium Phosphide HEMTs have demonstrated the best noise performance at cryogenic temperatures in the microwave frequency range of all active semiconductor devices, together with extremely low power consumption. For certain applications noise is not the only factor affecting the sensitivity. For example, gain fluctuations may play a dominant role in wide band radiometers. Unfortunately some of the factors that have contributed to improve the noise temperature have degraded the gain fluctuations. The operation at cryogenic temperatures also increases the fluctuations. This paper describes the experimental results obtained at the Centro Astronómico de Yebes (CAY) in the development of wide band cryogenic amplifiers. Special attention is paid to the influence of the bias point in noise and gain fluctuations. InP HEMTs from different foundries were tested. The amplifiers developed will be used in the Herschel ESA mission radiometers and the Atacama Large Millimeter Array (ALMA) receivers.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2004; DOI:10.1117/12.547097 · 0.20 Impact Factor
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    Isaac López-Fernández · Carmen Diez · Juan Daniel Gallego · Alberto Barcia
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    ABSTRACT: EMCOR is a heterodyne receiver for the frequency range of 201 to 210 GHz. It has been designed for ground-based measurements of various minor constituents of the stratosphere involved in ozone chemistry. Since the aim was the detection of faint spectral lines, a superconducting tunnel junction has been chosen as mixer element and special care has been taken in developing the calibration unit of the system. The front-end is completed by a quasi-optical system, a solid state local oscillator with electronic tuning and a HEMT pre-amplifier. In the back-end an acousto-optical spectrometer is employed to analyse the signal. A PC controls the whole system. The instrument has been installed at a high mountain site in the Swiss Alps.
    International Journal of Infrared and Millimeter Waves 10/2001; 22(11):1555-1575. DOI:10.1023/A:1015091928090 · 0.67 Impact Factor
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    ABSTRACT: We present the results from a monitoring of the v=1 and v=2, J=1-0 28SiO 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 Astronómico 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.
    Astronomy and Astrophysics Supplement Series 11/1999; DOI:10.1051/aas:1999112 · 1.75 Impact Factor
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    ABSTRACT: We have been observing SiO masers in evolved stars at the Centro Astronómico de Yebes since 1984, using the Yebes 14m dish. With this telescope it is possible to ob serve the 7mm lines, i.e. the rotational transitions J=1-0 in different vibrational states Observations at :higher frequencies were also carried out with the IRAM 30m telescope at Pico de Veleta (Spain). The data include monitoring and systematic observations, as well as search for new maser transitions or exotic emitters. The theoretical interpretation of the results is being undertaken, with emphasis on the discussion of pumping mechanisms.
    Lecture Notes in Physics 01/1993; DOI:10.1007/3-540-56343-1_293
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    J. Alcolea · V. Bujarrabal · J. D. Gallego
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    ABSTRACT: The 14-m radiotelescope at the Centro Astronomico de Yebes was used to search, from August 1986 to February 1988, for v = 3, J = 1-0 SiO maser line from numerous long-period variables, including 31 Mira variables, six supergiants, one semiregular, and one IR object. This maser line was detected in six new emitters, including RR Aql, V Cam, R Cas, microCep, U Her, and R LMi, as well as in seven that were previously reported. The SiO line was monitored for one and a half year in three sources, and the degree of linear polarization of the emission was estimated in two stars. The results of these observations indicate that the v = 3 line is about 35 times weaker in peak flux, 65 times weaker in profile area, and significantly narrower than the v = 1,2 lines. On the other hand, the variability and the degree of polarization are similar in these three lines. These results are compatible with the SiO masers being located in the circumstellar envelope.
    Astronomy and Astrophysics 01/1989; 211:187-198. · 4.48 Impact Factor
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    ABSTRACT: A fully sampled map of the J = 5 yields 4 line of HC3N has been made toward OMC-1 with an angular resolution of 2 arcmin. Two molecular clouds adjacent to the BN/KL region with radial velocities of 8 and 10 km/s are found. The 8 km/s cloud is more extended in the northwest direction than previously reported. The relationship between these two clouds and the molecular outflow is discussed.
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    ABSTRACT: The authors present observations of the SiO maser emission at 43 GHz and of the SiO thermal emission at 87 GHz from evolved stars. As a reference, they have also observed the 115 GHz line of CO, a good tracer of circumstellar matter. The authors conclude from their observations that both maser and thermal SiO emission in M-type stars are probably generated in an extended inner region (radius &lap;10 R*), in which the grains are still not completely formed. Physical conditions for this inner envelope are derived.
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    Juan Daniel Gallego · Isaac López Fernández